Physics 1 FINAL

Does dose rate increase or decrease with FFF

Increase

IONIZATION Ionization is the addition or removal of an electron from orbit. • In therapy context, it is almost always removal • Requires the application of energy. Ionization results in an __ pair: __ - the freed electron __ - the remaining atom that has lost the electron

Ion Negative ion Positive ion

Four methods for detecting ionizing radiation: __ collected to produce signal. Amplification of __ to produce stronger signal. __ of a substance that has absorbed energy from radiation. Radiation-induced __

Ions Ionization Fluorescence Chemical reactions

Kinetic energy equation

KE=1/2mv^2

No mass or charge. High let or low

Low

Mass Attenuation Coefficient equation

MAC= μ/density

What are the 2 pieces of equipment of choice for pt dosimetry cuz it can measure the beam delivered for tx and can give us a real time reading

MOSFETS and diodes

Electron beam MU equation:

MU= Prescribed tumor dose/DD x Ccal x Cfs x ISC DD: prescribed isodose Ccal: Machine calibration factor Cfs: cone/field size output factor ISC: inverse square correction factor (SSD, only matters if its not 100cm)

A source of microwave power to accelerate electrons. (Best for energies <10MeV)

Magnetron

Represents the probability per unit mass length of the filter that any one photon will be attenuated

Mass Attenuation Coefficient

Electron interactions with matter differ from photon beams because electrons have a __ &__

Mass and charge

The mass of an atom is not exactly the sum of the weights of the atom's subatomic particles. Some mass is used as energy to hold the atom together. This differential is called the __- __.

Mass deficit

• The depth at which electron equilibrium occurs has 6 other names

Maximum Dose Dmax Given Dose Entrance Dose Applied Dose Peak Absorbed Dose

Skin Sparing An inherent characteristic of __ beams. Maximum dose or peak dose is delivered below the skin surface. Skin no longer a dose limiting structure.

MeV

3 general purposes of radiation detection devices? __:Monitor radiation/activity of the beam __:Monitor radiation exposure in people __:Identify whether radiation is present

Measurement Protection Search

What does MOSFET stand for?

Metal Oxide Field Effect Transistor

Does compton scatter depend on atomic number of material?

NO

Is coherent scatter applicable in radiation therapy

Nah, maybe during sim

Do we use a narrow beam or a broad beam?

Narrow hella collimated

2 units for force

Newton or 1kg x m/s2 (m is sqaured)

Indirectly Ionizing Radiation Has a charge or no? First, a charged __ is created and released; • Second, the charged particle deposits energy through Coulomb interactions • Examples: X-rays, Gamma Rays, Neutrons

No charge Particle

Discovered on November 8, 1895, by Roentgen • Mass or no? • Charge or no? • Travel in straight but diverging lines • Travel at the speed of __ (in avacuum) • Can/cannot be focused • Give up energy to matter slowly through collisions with __ (exponentially attenuated by matter)

No mass No charge Light Cannot Atoms

Has/no mass, Has/no charge •Affected/unaffected by gravity •Affected/unaffected by electric fields •Affected/unaffected by magnetic field •Travel in straight but diverging lines at the speed of __ •Can/cannot be focused •Exponentially/not attenuated by matter

No mass, no charge. Unaffected Unaffected Unaffected Light Cannot Exponentially

Gamma rays originate from the __ of an atom whereas photons arise from the __ __.

Nucleus Orbital Shells

Gm detectors operate at high or low voltage?

Operates at a much higher voltage than ion chambers. these are just indicators of radiation. not precise measurements like ion chambers. good for surveying people, rooms, packages, tools, etc

Electron Blocking and Output: Blocking impacts the __ factor and __ dose distribution. When the diameter of the electron beam field is less than the __ range, there is a decrease in dose --Irregular blocking has a more significant impact Output readings must be taken when: ◦ If blocking is more than __% of the field ◦ If the __ is blocked ◦ If field is at an __ distance

Output, depth Practical 25% Central axis Extended distance

Potential energy equation

PE=mgh

Defined as the lateral distance between 2 specified isodose lines at a specified depth.

PHYSICAL PENUMBRA

Energy converted to mass and then back to energy. Which interaction?

Pair production

Photon interacts with nucleus. Complete absorption. Which interaction?

Pair production

Attenuation is the opposite of what

Penetration

Monochromatic = Monoenergetic = Homogeneous All photons have the same energy Attenuation results in a change of beam quantity/quality but NOT beam quantity/quality. The number of photons and total energy of the beam changes by different/the same fraction

Quantity Quality The same

What helps the device reset quickly before next discharge? Like combats dead time. Stuff inside the tube. suppresses electrical discharge. Absorbs secondary photons creates

Quenching agent

Most traditional units start with what letter

R

So chart of like voltages at what these devices work at. Theres I, P, CD, GM, and R. put them in order think thats ion recombination Proportional counter region Geiger muller Ionization chamber region Idk what cd is rn

R, I, P, GM, CD

Electron Beam Ranges R__ = The depth of Dmax R__ = Therapeutic Range or Useful Range ◦ The depth in cm of the __% isodose line Equation for therapeutic/useful range? Rp = __ Range ◦ The depth in cm at which point the electrons have stopped and nearly reached zero. Equation? R80 = __ Depth Equation? D50 = __ energy of the beam at the surface Equation?

R100 R90, 90% Depth of R90= Mev / 3.2 Practical ◦ Depth of Rp = Mev / 2 Treatment ◦ Mev/ 2.8 Mean ◦ D50 = Depth of the 50% isodose line (in cm) X 2.4

Gas filled chambers determine radiation exposure based on the __ and __ of ionization. Rate in counts/minute. Level in mR/hour

Rate and level

Diagnostic and low energy treatment unit targets are reflectance/transmission targets

Reflective

Gamma rays have same/different characteristics as x-rays

Same No mass • No charge • Travel in straight but diverging lines • Travel at the speed of light (in a vacuum) • cannot be focused • Give up energy to matter slowly through collisions with atoms (exponentially attenuated by matter)

same column of periodic table means ...

Same number of valance electrons

Scanning beams are used in place of __

Scattering foil

Limit of number of electrons in each electron shell is found by what equation

2n^2

The primary collimator creates what dimensions at iso? Can we control it?

40x40 We cannot control

1 Gray is equal to how many Sievert? A. 1 Sv B. 10 Sv C. 100 Sv D. 1000 Sv

A

How much voltage does a proportional counter uses in comparison to an ion chamber?

A little more than an ion chamber

Gravitational potential energy depends on what 2 things?

Height and mass

Are monochromatic beams attenuated at the same rate or varying rates?

The same rate

When moving deciminal to left and the exponent is negative, is the exponent gonna increase or decrease,

The whole number will decrease

Photon passes through absorber unaffected Photons that make it through a medium with no change in energy or direction

Transmission

Does a reflectance target or a transmission target waste less energy?

Transmission targets waste significantly less energy

Natural force that Holds nucleons together

Weak Nuclear

If distance is doubled, intensity will be __

reduced to 1/4

VAN DE GRAAFF GENERATOR ‐ 1937 "__ Generator" Electron source produces __ that are carried by a belt to the __ where potential difference or voltage is accumulated. Electrons are accelerated by dropping them through a series of __ before hitting the target. Produces photon beams up to __ MV Equipment was very small/large, difficult to house and shield.

"Electrostatic generator" Electrons, filament rings 2 MV Large

1 R = __ rad in air

.876

For most of the radiation used in medicine (X Rays, , e-), QF is = __

1

Distance is __ dimensional Area is __ dimensional Volume is __ dimensional

1 2 3

Baldwin farmer ionization chamber Benefits compared to condenser R meter: Reduces stem effect to less than __% Less likely to lose a charge if __ Gives a real-time or instant __ Able to clear the __ outside the room

1 Bumped Readout reading

1 Gy = ____ J/kg

1 J/kg

MEGAVOLTAGE UNITS Units that create energies of __ Mev (__ ev) or higher Van De Graaff Generator Cobalt‐60 Linear Accelerator Betatron Microtron Cyclotron

1 Mev (10^6ev) or higher

1 cGy = _____ rad

1 rad

1. Find the practical range for a 9Mev beam. 2. Find the therapeutic range for a 16Mev electron beam. 3. Find the mean energy at the surface for an electron beam whose 50% isodose line is at a depth of 4cm.

1. 4.5cm 2. 3.2 cm 3. 9.6MeV

Label the picture

1. Electron beam 2. target 3. Primary collimator 4. Flattening filter 5. Scattering foil 6. Slot for wedges, blocks, compensators 7. Patient 8. Flattened x-ray beam 9. Secondary collimator 10. Ion chamber

6 steps before Using survey instruments

1. May require warm up time (Approximately 5 minutes) 2. Check device for physical damage 3. Check calibration sticker to ensure it is current within one year 4. Check battery level 5. Zero device 6. Perform source check

Label the picture

1. electron beam 2. target 3. Primary collimator 4. Flattening filter 5. Secondary collimator 6. Electron applicator 7. Accessory mount 8. Ion chamber 9. Carousel 10. Scattering foil

PAIR PRODUCTION Incoming photon with at least __MeV interacts with the electric field of an atomic nucleus As the photon approaches the nucleus of the atom, its energy changed into __ (in the form of a negatron and positron) Negatron eventually __ Positron collides with a free electron (Pair Annihilation) Positron and free electron are destroyed and their energy is re-emitted as two __MeV photons traveling 180° from each other (mass converted back to energy) This interaction is an example of the E=mc2 principle Energy converted to mass and then back to energy

1.022 Mev Mass Comes to rest .511 Mev

A person receives a dose of 1.8Gy from x-ray radiation. What is the equivalent dose?

1.8 Sv

COHERENT SCATTER Low energy photon (<__KeV) passes near an outer orbital electron Photon does not have enough energy to cause ionization Atom's electron absorbs the incoming photon, causes vibration, re-emits photon with same energy in a slightly different direction No energy transfer = no ionization = no biological effect

10

PHOTONUCLEAR INTERACTION Threshold energy of incoming photon is __-__Mev High energy photon is absorbed by the __ of an atom Atom becomes radioactive & emits a neutron (or another nuclear particle) Occurs in high/low atomic number materials at high energies, though the probability is quite low, even when photon energy meets or exceeds the threshold of __-__MeV Not important interaction in tissues which have a low Z# Responsible for "activating" treatment unit components. This interactions happens in like the jaws of the machine. Neutrons moderated by __ __ and __ (hydrogenous materials)

10-15Mev Nucleus High 10-15Mev borated polyethylene and wood

1 rad = __ ergs/g

100

1 Air kerma = ___ R

100 R

Determine the dose in air if an exposure reading measures 100R.

100 R x .876cGy/R = 87.6cGy

1 Gy = ___ rad

100 rad

1 Sv = ___ rem

100 rem

When pair production happens, what is the average energy of the beam? What is the singular minimum energy for this interaction to happen?

10Mev ish 1.022 Mev

Find the exposure in Roentgen if the absorbed dose per unit mass of air is 100cGy.

114.55R

Atomic number is 131 and atomic mass number is 54. How many neutrons are there?

131-54=77 neutrons

ORTHOVOLTAGE UNIT Beam energy of __-__kV SSD of __cm For many years provided the most penetrating beams Uses changeable filters made of __ to harden the beam __ used to define field sizes & __ used to adjust the field sizes Called "__ therapy" -At __cm the dose is 90%

150-500KV 50cm copper cones, diaphragm deep therapy 2

Electron Beams and Extended Distance: Extended distance defined as no more than __cm beyond standard SSD. Electron beams do not follow inverse square as effectively as photon beams. Extended distance does not impact __ much; __ and __ is more significantly impacted. 2 methods for correcting output due to extended distance?

15cm Extended distance does not impact depth dose much; output and penumbra is more significantly impacted ◦ Effective Point Source ◦ Virtual SSD Method

Limit of electrons in the M shell

18

If 1cm bolus is used for an electron beam, dmax will move __cm toward the surface

1cm

Electron Collision Interactions and Energy Loss: Typical Energy Loss: --In water (soft tissue), energy loss by collision interactions is about __MeV/cm for 1‐100MeV electron beams. ◦ Example: How much energy loss will occur if a 12Mev beam passes through 4cm of tissue

2 Mev/cm It will lose 8 Mev through 4cm of tissue

A person receives 2Gy of 8MeV electron radiation. What is the equivalent dose?

2 Sv

1 R = __ c/Kg

2.58 x 10^-4

GRENZ RAY UNIT Provides energy of less than __kV __ SSD Used to treat __ Treatment associated with a very high/low skin doses Quality measure in half‐value layer expressed in millimeters of __

20KV 0 Very superficial skin lesions High Aluminum

Speed of light = what? One equation for no vacuum and one for in vacuum

3 x 10^8 m/s or 3 x 10^10 cm/s in a vacuum

TREATMENT COUCH • May be referred to as the tabletop or the patient support assembly • Mounted on a rotational axis around the isocenter • Many support up to __lbs and range in width from __ to __ cm • Indexed carbon fiber couch • Robotic table allows __ degrees of freedom

300 lbs 45-50cm 6

1 C/kg = ____ R

3876 R

TLD PREP & READING PROCESS TLDs annealed (heated) @ __° C for 1hr and __° C for 2hrs -Empties traps TLDs placed & irradiate TLDs removed from wrappers TLDs pre-annealed @ __ °C for 10min TLD read individually in reader -Done in a light proof chamber with __ Dose calculated using calibration factor

400, 100 100 photomultiplier

A person receives a dose of .2Gy from alpha radiation. What is the equivalent dose?

4Sv

Electron Beam Blocking: Blocks must reduce transmission to less than __%. Thickness in mm can be estimated in LEAD by: ◦ What equation? (per Khan) ◦ How to find thickness in CERROBEND? Cone/block must be a minimum of __cm from patient's surface ◦ This reduces useless skin dose from __ ◦ Also reduces penumbra by increasing the SDD or SCD

5% ◦ MeV/2 +1mm (per Khan) multiply lead thickness (from above) by 1.2 5cm Scatter

MULTILEAF COLLIMATOR (MLC) • __-__ leaves • Located below __ • Computer‐driven • MLCs can move during treatment Concerns compared to cerrobend blocks: --Physical __ is greater --Interleaf transmission leakage is __% ‐ __%

52‐160 secondary collimation Penumbra 2.5% ‐ 4%

HVL is 3 mm of copper. What % beam will get through 12mm of copper?

6.25% after 4 HVL's

What is planck's constant

6.63x10^-34

Varian True Beam - "High Intensity Mode" • Flattening filter mode • 6, 10, and 15 MV photons • Dose rate = __MU/minute • Flattening filter free mode • 6 and 10 MV photons • 6MV Dose Rate = __MU/minute • 10MV Dose Rate = __MU/minute

600 1400 2400

COMPTON SCATTER Occurs at energies of __kVp-__MeV. Predominant interaction about __keV - __MeV Incoming photon interacts with an inner/outer shell electron which is loosely bound (called a "__ electron") Incoming photon energy is much larger than binding energy of electron Some energy is given to the outer shell electron, and it is ejected (called __ or __ electron) Some energy is retained by the incoming photon which is now changed in wavelength (energy) and direction (ie: scattered)

60kvp-10Mev 500kev-10Mev Outer, free Recoil or compton

Find the absorbed dose per unit mass of air exposed to 75R

65.7 rad or 65.7cGy

VALENCE • Number of electrons in the outer most orbital shell • Determines the chemical activity of an element No more than __ electrons can be in the valence orbital shell

8

BEAM FLATNESS The maximum variation of the beam intensity in the central __% of the beam, measured at a depth of __cm or the depth of the __% isodose line

80% 10cm 50%

Characteristics of Electron Beams: Rapid dose fall‐off --Rate of change of the value or dose with a change in position is termed gradient ---Beyond __-__% there is a rapid fall‐off of dose Surface dose is about __%‐__% --As electron energy increases, surface dose & depth dose __ --3 things that also impact surface dose? ---Field size diameter should not be less than the __ range Brems Tail increases/decreases with increased electron energy --Results when high/low energy electrons interact with high Z material

80-90% 80-100% Increase Scattering system, atomic number of absorber, field size and collimator Practical Increases High

For 1MeV photons, what is the dose delivered to muscle if the exposure to that muscle is 90R? (Use 7.3 table)

86.59cGy

gravity is equal to what

9.8 m/s2

SPECIAL CASES OF COMPTON 90-Degree Scatter: • Scattered photon emerges at __-degree angle to the __ • If scattered at 90 degrees, has a max value of __MeV

90 Incident photon .511Mev

2 kinds of bending magnets. Function?

90 degree and a 270 degree Changes direction of electron flow

Special case of compton scatter that involves: • Scattered photon emerges at 90-degree angle to the incident photon • If scattered at 90 degrees, has a max value of .511MeV

90 degree scatter

For 10MeV photons, what is the exposure delivered to bone that results in an absorbed dose value of 90cGy? (Use 7.3 Table)

91.19R

For 10MeV photons, what is the dose delivered to soft tissue (water) if the exposure to that tissue is 105R? (Use 7.3 table)

99.23cGy

PHOTOELECTRIC EFFECT Occurs with energies <__MeV (around __-__keV) An incoming photon is absorbed by an inner/outer shell electron Photon's energy transferred to the __ If energy is less/more than binding energy of electron, electron is ejected as __ Photoelectron has kinetic energy equal to __ minus __ Ejected electron leaves a void Void filled by outer electron, possible emission of characteristic radiation __ electron possible, causing another ionization in atom

<1MeV, around 50-500 KeV Inner Electron MORE, photoelectron Incoming photon energy minus binding energy of the electron Auger

An electron beam is calculated to deliver 200cGy using 239MU. If the beam terminated after delivering 115MU, what dose was actually delivered?

= 96.23cGy

A prescription calls for a 9MeV beam to deliver 300cGy to the depth of the 95% isodose line. Based on the cone size and extent of blocking, the field size output factor is 1.05 and the unit is calibrated to deliver 1.2cGy/MU.

=251 MU's

A prescription calls for a 12MeV beam to deliver 250cGy to the depth of the 80% isodose line. Based on the cone size and extent of blocking, the field size output factor is 1.012 and the unit is calibrated to deliver 1cGy/MU.

=309MU's

A vertically‐mounted accelerator structure provides a short distance to accelerate the electrons in a low energy machine and a horizontally mounted accelerator structure provides a longer distance to accelerate electrons and equates to a higher energy machine. A. True B. False

A

At what rate does the Cobalt 60 source decay? A. 1% per month B. 2% per month C. 3% per month D. 5% per month

A

In treatments using kilovoltage equipment, filters are used to: A. Filter low‐energy x‐rays B. Shield the patient from all radiation exposure C. Collimate the beam D. Increase the quantity

A

Of the following treatment units, which has the least amount of skin sparing? A. Orthovoltage B. Cobalt C. 4 MV Beam D. 10 MV Beam

A

What is the average energy of the gamma rays emitted by a Cobalt‐60 teletherapy unit? A. 1.25MeV B. 1.17MeV C. 1.33MeV D. 2.5MeV

A

What kind of accelerating guide? Provides maximum reflection of the waves at both ends of the structure. The combination of forward and reverse traveling waves will give rise to stationary waves. Energies of forward and reverse combine. Amplitude is sum of both of them. Increases energy without increasing length of the tube

ACCELERATOR GUIDE: STANDING WAVE ACCELERATOR

What kind of accelerating guide? The traveling wave structure requires a terminating or "dummy" load in order to absorb the residual power at the end of the structure, thus preventing a backward reflected wave.

ACCELERATOR GUIDE: TRAVELING WAVE ACCELERATOR

A secondary effect of characteristic x-rays The energy from the characteristic photon may impart its energy to an outer shell electron, which then is ejected from the atom

AUGER ELECTRONS

• The amount of energy from ionizing radiation absorbed in matter per unit mass of irradiated material at a specific point

Absorbed Dose

Equation for effective dose

Absorbed dose x Wr x Wt

Attenuation: Reduction in intensity of a beam Combination of __ and __ Influenced by __ and __

Absorption and scatter Beam energy and absorber composition

Receives microwave power and combines power with injected electrons • Accelerates electrons as they pass through electromagnetic fields to almost light speed • Traveling‐Wave Accelerator • Standing‐Wave Accelerator

Accelerator Guide

What are the 4 forms of high let radiation

Alpha Particles • Neutrons • Protons • Heavy Recoil Nuclei

What are the 4 particulate radiations

Alpha particles Beta particles (electrons) Neutrons Protons

Do we deal with more elastic or inelastic interactions?

Always inelastic

KERMA Kinetic Energy Released in Matter • Amount of energy transferred to __ by __ • Indirectly ionizing radiation imparts energy to matter in a __-step process • Is it a measure of energy deposited into tissue at depth?

Amount of energy transferred to electrons by incoming photons • 2-step process • NO

Calibration of ion chambers All radiation detectors must be calibrated when? Calibration consists of 2 parts: 1. __ - checks device on mechanical level 2. Chamber is exposed to a known, calibrated, uniform __ to confirm accurate reading Unsealed chambers sensitive to pressure & temp: Increase/decrease in air temperature = decrease in number of ionizations or decreases sensitivity of the chamber Increase/decrease in air pressure = increase in number of ionizations or increases sensitivity of the chamber

Annually and any time a repair is made. Pre-calibration Radiation field Increase Increase

PROBABILITY OF PAIR PRODUCTION Depends On what 2 things?

Atomic number Energy of incident photon

Atomic number vs electron density

Atomic number is the number of protons in the nucleus and electron density is the amount of electrons present per kg?

Reduction in intensity of a beam

Attenuation

A secondary effect of characteristic x‐rays. The energy from the characteristic photon may impart its energy to an outer shell electron of the same atom, which then is ejected from the atom This ejected outer shell electron is called an __ __

Auger Electron

• Contains emergency off button

Auxiliary Power Distribution System

A patient is to be treated with a 7MeV electron beam. How thick (in centimeters) should a LEAD shield be to reduce the dose to less than 5% of the useful beam? A. 3 cm B. 4.5 cm C. 5.5 cm D. 6 cm

B

Of the following treatment units, which has a Dmax depth of 1.5cm? A. 4MV beam B. 6MV beam C. 10 MV beam D. 15 MV beam

B

The electron gun is considered the: A. Anode B. Cathode

B

What is the SI unit for absorbed dose? A. Rad B. Gray C. Sievert D. Rem

B

Which of the following is true when the linear accelerator is in the electron beam mode? A. A flattening filter is required to make the electron beam profile symmetric and flat B. A scattering foil is required to make the electron beam profile symmetric and flat C. There is an interaction with the transmission target before leaving the exit window D. The ionization chambers are retracted for electron treatments

B

The maximum variation of the beam intensity in the central 80% of the beam, measured at a depth of 10cm or the depth of the 50% isodose line

BEAM FLATNESS

what machine? Accelerates electrons within a hollow ring or doughnut

BETATRON ‐1941

Phenomenon of high dose at the end of the travel of high LET particles • Dense volume of ionizations are produced at the end of the particles track

BRAGG PEAK

Adjacent Fields: When fields abut, treatment planners must consider the __ effect of the isodose lines ◦ If a skin gap is used, there will be an underdose at __ ◦ If no skin gap is used, there will be an __ at depth (hot spots) ◦ May __ the match which simply means the point of the match line is changed by .5cm - 1cm on a scheduled basis

Ballooning Depth Overlap Feather

Linear Attenuation Coefficient affected by what 3 things?

Beam energy Electron Density of the absorber (state of the absorber (gas solid liquid)) Atomic number

HVL depends on what 2 things?

Beam energy and density of material

2 factors that influence depth of Dmax? One really effects it and one kinda does

Beam energy effects it most Field size kinda effects it

• The gantry rotates on a horizontal axis on __ within the drive stand

Bearings

COBALT‐60 UNIT ‐ 1951 The source material undergoes __‐ decay Results in excited daughter nuclei that emit a __ and two __ to attain ground state of __ Beta Emission of __MeV - absorbed by capsule Two gamma rays are emitted: -__Mev and __Mev -Effective/Average Energy = __Mev __ year half life Decays about _1% per __ Associated with small/large penumbra __ setting is calculated, not MU setting

Beta beta, gamma, Nickel-60 .31MEV 1.17 and 1.33 MeV Average= 1.25 5.27 per month large timer

ATOMIC MODELS • The currently accepted model the "__ Model" named after Neils __: • Electrons orbit __ within shells • Shells from inner to outer are named __,__,__.... • __ is central component • Electrons remain in orbital shells as a result of strong forces of attraction between the __ and __.

Bohr, Bohr Nucleus K, L, M,... Nucleus Electrons and nucleus

Beam Attenuation Changing quantity or quality of polychromatic radiation beams? More low/high energy photons are removed, results in beam hardening

Both Low

ION CHAMBER • Ionization chamber embedded into the machine; built into the path of beam • Measures and monitors electron or photon beam output? • Monitors/samples the beam for its __ in the right/left and inferior/superior direction • Produces __ that terminate the beam when the prescribed dose is given • Linacs employ __ chambers with different power supplies and electrometers.

Both Symmetry Electrical signals At least 2

What theory Allows for measurement of absorbed dose in medium where Roentgen no longer applies • Relates absorbed dose in device medium (cavity) to the absorbed dose in the medium surrounding the cavity

Bragg Gray Cavity Theory

Most of the radiation therapy beam consists of __ Radiation

Brems

What kind of process produce characteristic and brems? Different type for each

Brems is radiative process. Characteristic is collision process.

What part of the isodose curve is the photon radiation part of our electron beam due to photon contamination?

Brems tail

A patient has a tumor at a depth of 4cm. What energy of electron beam should be used so that the 80% isodose line encompasses the tumor? A. 8MeV B. 10MeV C. 12MeV D. 14MeV

C

A patient is to be treated with a 15 MeV electron beam to a treatment volume that measures 10 cm in width and length at depth. Select the best field size for this treatment: A. 10 x 10 cm B. 11 x 11 cm C. 12 x 12 cm D. 13 x 13 cm

C

As a radiation therapist, you witness the table begin to rise after the correct dose has been delivered for the first treatment field. You press the emergency off button located on the wall near the gantry, but nothing happens, what do you do next? A. Tell the patient to jump off the table B. Allow the table to continue rising C. Shut off the main circuit breaker to the room D. Call out for the physicist

C

Depth of maximum dose for a 10MV beam is _________ below the skin surface. A. 0.5 cm B. 1.5 cm C. 2.5 cm D. 5 cm

C

Determine the mean energy of an electron beam at the surface, whose 50% isodose value is at a depth of 5cm. A. 8MeV B. 10 MeV C. 12 MeV D. 14 MeV

C

The f-medium factor is a function of: I. composition of medium II. energy of photon beam A. I only B. II only C. I and II D. Neither

C

What is the range in tissue for a 12‐MeV electron beam? A. 3 cm B. 4 cm C. 6 cm D. 8 cm

C

Which of the following is NOT found inside the head of a linear accelerator? A. Ion Chambers B. Target C. Accelerator Structure D. Scattering Foil

C

Which of the following is the half‐life of a Cobalt‐60 source? A. 30 years B. 1600 years C. 5.27 years D. 74.2 days

C

CONTACT UNIT Beam energy of __-__kV SSD of __cm‐__cm Uses what material? filters to harden the beam Used to treat deep/superficial lesions (__ - __cm depth). Low/high energy, short/long distance, decrease/increase in depth dose At __ cm depth there is less than 10% of the dose Delivers a low/high skin dose

CONTACT UNIT Beam energy of 40‐50kV SSD of 0cm‐2cm Uses aluminum filters to harden the beam Used to treat superficial lesions (.5 - 1cm depth). Low energy, short distance, decrease in depth dose At 2cm depth there is less than 10% of the dose Delivers a high skin dose

what machine Accelerates heavy charged particles

CYCLOTRON

Mosfet detectors A type of solid-state detector Used for in vivo dosimetry and profile measurements: -Surface dose -Intracavitary dose -Can/cannot be used for absolute dosimetry Advantages: -Direct reading -Thin active area <__mm -Dose rate independent -One detector for multiple __

Cannot <2mm Energies

•Processes Resulting in X‐ray Beam Production •Collision processes yield __ Radiation •Radiative processes which yield __ Radiation

Characteristic Bremsstrahlung

Linear Energy Transfer (LET) • Average energy deposited per unit path length • Defines the rate at which energy is deposited by __ particles (incident or secondary) while traveling through matter • The higher the LET, the more/less biologic damage • Increase LET = Increase/decrease RBE • 3 kinds Low LET Radiation? • 3 kinds of High LET radiation?

Charged More Increase Low= x-rays, gamma rays, and electrons/betas High= neutrons, protons, alphas

Valve that prevents backflow of microwave power

Circulator

ELECTRONBINDING ENERGY Electron binding energy (Coulomb force) is the energy needed to hold an electron in an orbital shell • The closer/further the orbital shell is to nucleus; the higher the binding energy • As Z number increases; the lower/higher the binding energy • To achieve ionization, energy lower/greater than the binding energy must be applied to the atom • Binding Energy can be overcome by the addition of __ to the atom

Closer Higher Greater Energy

What interaction with matter just causes the electron to vibrate. Photon is reproduced in a different direction. Doesnt give up any energy. All energy remains

Coherent scatter

What are the 5 interactions with matter?

Coherent scattering Compton scattering Photoelectric absorption Pair production Photodisintegration

Collision or radiative? Electron interacts with electrons of the absorber material ◦ Primary interaction with Low Z material ◦ Low Z = higher electron density, more opportunity for collisions

Collision

What is the Primary way electron beams lose energy in radiation therapy energy ranges

Collision Interactions

2 main electron interactions with matter. Are the elastic or inelastic interactions?

Collision and radiative. They are both inelastic

What are the two things we have at the end of a compton scatter reaction

Compton electron and scattered photon

Thompson and simple scatter are referring to what

Compton scatter

What interaction is most common in radiation therapy delivery

Compton scatter

THIMBLE IONIZATION CHAMBERS Types: __- thimble chamber connected to condenser which stores a charge. __ - thimble chamber connected to an electrometer; provides instant reading. Chamber Walls constructed of __ __ used to increase efficiency when measuring high energy radiation. -Cap made of air or tissue equivalent material -Thickness depends on photon energy -Establishes electron __ to allow the same number of electrons being liberated to be captured.

Condenser R meter Baldwin Farmer Condensed air Build-up cap Equilibrium

Allows equipment to operate at a constant temperature

Cooling Systems

Electron Radiative interaction with matter: Electrons interact with the __ of the absorber material nuclei ◦ Occurs with high/low Z material; Leads to __ production ◦ High/low Z = More protons = Stronger Coulomb Force

Coulomb force High, brems High

Difference between covalent and ionic bonds

Covalent bonds involve the sharing of electrons between atoms Ionic bonds involve an atom giving a valance electron to another atom to stabilize them both.

3 laws of conservation of energy Energy is never __ or __. It can change from one __ to another. Total amount of energy in a closed system is __.

Created or destroyed. Form. Constant.

Simple parallel plate ion chamber: Air molecule ionized. Electrodes on both sides. Higher voltage=faster ions will move. Rate of __ is indicating the ion rate that is happening in ionization chamber.

Current

The circulator in the linear accelerator does which of the following? A. Monitors the water temperature B. Spins the electrons in the right direction C. Conducts microwaves from the radiofrequency driver into the klystron D. Isolates the klystron from reflected microwave power

D

The flattening filter serves to: I. Shape the x‐ray beam in its cross‐ sectional dimension II. Create a more uniform beam at depth III. Broaden the electron beam making it clinically useful IV. Measure and monitor the beam intensity A. I only B. 2 only C. III and IV D. I and II

D

Which of the following BEST describes the order in which electron bunches and resulting photons travel through the head of a linear accelerator? A. Bending magnet, dose chambers, target, flattening filter, wedge B. Bending magnet, target, dose chambers , primary collimator, wedge, flattening filter C. Bending magnet, target, primary collimator, flattening filter, wedge, dose chamber D. Bending magnet, target, primary collimator, flattening filter, dose chamber, multi‐leaf collimator

D

A measure of beam energy and penetration • This ratio describes relative dose of radiation at any depth • Dose at depth / dose at Dmax. 2 names

DEPTH DOSE OR PERCENT DEPTH DOSE

A cooling time or when detector can no long work

Dead time

When dealing with scientific notation, if you move the decimal to the right, does the exponent increase or decrease if the exponent is positive?

Decrease

Equation for density

Density = mass/volume

Photoelectric effect is used mostly where

Diagnostic imaging

Difference of interactions with the body of an xray beam

Differential absorption

Chamber filed w solid semiconductor material

Diode detectors

Deposits energy through direct Coulomb interactions. Direct or indirect ionizing radiation?

Direct

Frequency & Energy have a direct/indirect relationship

Direct

3 special cases of compton scatter

Direct Hit Grazing Hit 90-Degree Scatter

Special case of compton scatter that involves: • Incoming photon has direct hit of atomic electron • Electron moves in same direction of incoming photon (0°) with most of the energy • Scattered photon will travel backwards (180°) with minimum energy of < .255MeV

Direct hit

Alpha particles, beta particles (electrons), and protons are directly/indirectly ionizing

Directly

MU & Dose Proportion: MU and Dose are directly/indirectly proportional Applies to photon and electron beams Can use a ratio to solve for the unknown Example: An electron beam is calculated to deliver 200cGy using 211MU. If the equipment terminates after delivering 171MU, what dose was actually delivered? Dose1 / MU1 = Dose2 / MU2 200 = x 211 171 X = 162cGy

Directly Dose1 / MU1 = Dose2 / MU2 200/211 = x/171 x=162 cGy

QUENCHING AGENT Agents used in the G-M tubes to suppresses electrical __caused by UV photons -2 Commonly used agents? Serves to prevent continuous __ Allows chamber to reset quickly before the next __

Discharge Chlorine or alcohol discharge discharge

electron equilibrium like main other name in bold

Dmax

Pros of TLD • Small • Reusable • Wide range of __ • __ rate independent • __ equivalent • No angular __ • __ beam can be measured appropriately

Dose Dose Tissue Dependence Oblique

= Absorbed Dose x Quality Factor (QF)

Dose Equivalent

If Linear Attenuation Coefficient goes up, does HVL go down or up

Down

If beam energy goes up, does Linear Attenuation Coefficient go up or down?

Down

If energy goes up, chance of photoelectric absorption goes up/down

Down

When energy goes up, the chance of coherent scatter goes up/down

Down

FINDING PHOTON ENERGY equation. What do the symbols mean?

E=hf Energy of the photon= planck's constant x Frequency of radiation

Equation for conservation of energy

E=mc2 Energy = Mass x (Speed of Light Constant)2 Speed of Light = 3 x 10^8m/s or 3 x 10^10cm/s in a vacuum

Defined as the point at which the energy of the electrons coming to rest equals the energy of the electrons being set into motion by new photon interactions.

ELECTRON EQUILIBRIUM

Energy applied to an atom can be given to an electron causing it to become unstable and thus raising it to a higher energy level • Not enough energy to eject the electron from orbit

EXCITATION

Sum of equivalent doses to all organs, each adjusted to account for the sensitivity of the organ to radiation• Provides the mean energy absorbed multiplied by the radiation weighting factor multiplied by the tissue weighting factor

Effective Dose, E

Which method for correcting output due to extended distance uses an effective ssd, not a virtual ssd? i think its just the creation of electron beam at an imaginary point

Effective Point Source Method

Elastic or inelastic interaction? Theres no loss of energy because the electron is giving up all of its energy. The kinetic energy is conserved because it wasnt lost it was just transferred to a different electron. If the total amount of kinetic energies of the particle and the atom are the same after the interaction then know that an elastic interaction has taken place. theres no loss of kinetic energy.

Elastic

The total kinetic energy before the collision is the same as the total kinetic energy after the collision

Elastic interactions

Is coherent scatter an elastic or inelastic interaction?

Elastic. All energy remains

EMR stands for what

Electromagnet radiation

Natural force that Causes the interaction between electrically charged particles • Opposite charges attract, Like charges repel

Electromagnetic

Radiation that comes from oscillating electromagnet waves?

Electromagnetic radiation

Fundamental force that is Electric and magnetic forces resulting from the motion of the electrically charged particles. Opposites attract, like-charges repel. Has short/long range.

Electromagnetism. Long range.

• Produces electrons • Injects electrons into the accelerator tube • Considered the CATHODE

Electron Gun

• __ (__) is the energy needed to hold an electron in an orbital shell. 2 names

Electron binding energy (Coulomb force)

The __ produces the electrons and injects them into the accelerating structure. The __ is where the electrons are accelerating depending on the energy we are trying to achieve. Because our accelerating structure is horizontal, we have the __ that directs electrons towards the patient. The x-ray target is moved out of the way. Primary collimator doesnt do much cuz electron beam is so small. Carousel rotates to put __ in place. 2 sheets of high atomic number material. one __ the beam and one makes the beam more __. Electron beam is considered monoenergetic till it hits the __. Thats when the energies start to vary due to scatter. __ is used to hold cones and cones hold the blocks. Electron applicator directs the electron beam towards the patient.

Electron gun accelerating structure Bending magnets Scattering foil broadens, uniform scattering foil Accessory mount Electron applicator

X‐rays are produced when high speed __ are suddenly decelerated

Electrons

BETATRON ‐1941 Accelerates __ within a hollow ring or doughnut Electron in a changing magnetic field experiences __ Accelerated electrons strike a target to create a photon beam and are extracted without hitting target to create an electron beam. Produces energies up to __MV 3 Disadvantages?

Electrons Acceleration 2 MV 1) lower dose rates 2) only small field sizes 3) very large equipment

Bragg Gray Cavity Theory • Allows for measurement of absorbed dose in medium where Roentgen no longer applies • Relates absorbed dose in device medium (cavity) to the absorbed dose in the medium surrounding the cavity • Considerations: • Cavity must be smaller than range of __ • Absorbing material must be greater than __ __ • Absorbing material and beam must be __

Electrons Electron equilibrium Homogenous

Electron collision interaction with matter: ◦ Electron interacts with __s of the absorber material ◦ Primary interaction with high/low Z material ◦ High/low Z = higher electron density, more opportunity for collisions

Electrons Low Z Low Z

Dense volume of ionizations are produced at the beginning/end of the particles track

End

The equation for relationship between energy and wavelength is:

Energy in ev= 1.24 x 10^-6 (ev)(m)/wavelength in m

PROBABILITY OF PHOTOELECTRIC EFFECT Depends On what 2 things?

Energy of incident photon Atomic number of absorbing material

PROBABILITY OF COMPTON Depends On what 2 things?

Energy of incident photon Electron Density

PROBABILITY OF COHERENT SCATTER Depends on what 2 things?

Energy of incident photon Atomic number

Forces provide __. Energy is the ability to do __. Work is the application of __ through a distance.

Energy. Work. Force.

Because most of the radiation used in medicine (X Rays, , e-) QF is = 1, the absorbed dose and dose equivalent are numerically different/equal

Equal cuz Dose equivalent is absorbed dose x quality factor. If our quality factor is 1 we're gonna be multiplying by 1

Difference between equivalent dose/dose equivalent and effective dose

Equivalent dose considers type of radiation and the dose Effective dose is equivalent dose x the tissue weighting factor

Defined as the number of ionizations produced in air

Exposure

Air Kerma • NCRP recommends that air kerma replaces the concept of __ • Air-kerma is related to the response of air to radiation • Equals the sum of kinetic energy of all __ __ liberated per unit mass • All about energy transferred to __ by __

Exposure Charged particles Electrons by photons

Roentgen to Rad (or cGy) Conversion aka exposure to absorbed dose conversion. Goal is to go from exposure to absorbed dose cuz they dont like exposure anymore

Exposure (in R) x Conversion Factor of .876cGy/R OR .876rad/R cuz 1 cGy=1 rad

refers to exposure produced per unit of time

Exposure Rate

Equation for dose in medium

Exposure x f medium factor (theres like a little chart that says the f medium factor of each beam with each material so its like a known thing)

What is TrueBeam's "high intensity mode" referring to

FFF

Makes the photon beam more uniform at depth

FLATTENING FILTER

100 Gray = 1 rad A. True B. False

False

• Cools power distribution component

Fan Control

3 parts of modulator cabinet

Fan control Primary power distribution system Auxiliary power distribution system

Narrow Beam Geometry Very small beam (highly collimated) Attenuator close/far from detector A lot/a little scatter reaches detector

Far A little

How to find exposure?

Figured by counting how many ions are created with an ion chamber

•Serve to absorb low energy photons of heterogeneous beams. •Removes unwanted or useless low energy photons from beam •Results in beam hardening; where the # of photons decreases but the average energy or quality of the beam is increased

Filters

What are the 2 Laws of electrostatics (Coulomb's laws)

First Law: Like charges of electricity repel each other, whereas unlike charges attract each other. Second Law: The force extended between two small charged bodies (point charges) is directly proportional of their charges and inversely proportional to the square of the distance between them

Directs the beam at a patient's tumor

GANTRY

Defined as lower energy radiation at lateral edges of a field

GEOMETRIC PENUMBRA

Just like xray photons but come from the nucleus of an atom

Gamma rays

3 general kinds of radiation detection devices

Gas-Filled Chambers Solid State Detectors Neutron Dosimeter

which detector? Has a gas filled tube: electrode that goes in the middle of probe and provides a charge. probe is filled with inert gas. gas is ionized. electric field is so strong that a single ionization leads to massive cascade event. single ionization, ionizes all atoms in the probe. very sensitive. can detect low energy or a single photon. must charge/reset after each reading=down time.

Geiger muller

What is the geometric penumbra for a Cobalt unit if the source size is 2cm, the SSD is 100cm, and the SDD is 50cm?

Geometric Penumbra = SS x {SSD + d ‐ SDD} / SDD Geometric Penumbra = 2 x {100- 50} / 50 Geometric Penumbra = 100 / 50 Geometric Penumbra = 2.0 cm

What are the 4 fundamental natural forces that is responsible for the way an atom behaves and functions?

Gravitation Weak interaction Electromagnetism Strong interaction

Natural force that is the Attraction between two objects

Gravitational

What is the weakest fundamental force? Why is it an attraction force?

Gravitational force. It is always trying to pull things together.

Special case of compton scatter that involves: • Incoming photon has a grazing hit of atomic electron • Causes very little energy loss • Most of the energy is carried away by the scattered photon, which will have nearly the same energy as the incident photon

Grazing hit

Symbol for dose equivalent

H

A specific thickness of material that reduces the beam intensity to exactly half of its original intensity

HalfValue Layer (HVL)

Filters •Serve to absorb low energy photons of heterogeneous beams •Removes unwanted or useless low energy photons from beam •Results in beam __; where the # of photons increases/decreases but the average energy or quality of the beam is increased/decreased •Target provides this filtering effect for kilovoltage/megavoltage units •Higher/lower energy units may use filters of various kinds •Thoraeus Filter :Tin (tube), Copper, Aluminum (patient)

Hardening Decreases Increases Megavoltage Lower

CYCLOTRON Accelerates __, __ particles __, __, or __ are accelerated in a spiral path by alternating current between two semi‐circular __. __ beam requires no target. __ beam requires bombardment of beryllium target.

Heavy, charged Protons, neutrons, or deuterons Dees Proton Neutron

Particles that have substancial mass and usually a charge. High or low let

High

SECONDARY COLLIMATOR • Movable jaws that shape the beam in x and y directions to define a rectangular field. • Made of high/low Z material. 2 examples? Maximum field size in modern units is 40cm x 40cm • MLC's or Cerrobend blocking may further define field

High Tungsten and lead 40cm x 40cm

Linac target: Made of high/low atomic number material like __ • Referred to as a __ target • Considered the anode or cathode? • In place when programming a electron/photon beam Collision Interactions=__ radiation Radiative Interactions=__ radiation • Retracts from path of electron beam from bending magnet when programming an electron beam

High, tungsten Transmission Anode Photon Characteristic Brems

Beam Direction Megavoltage treatment unit targets are reflectance/transmission •Higher/lower the energy results in less angular spread.

Higher

Higher Linear Attenuation Coefficient= Lower/higher chance of being attenuated?

Higher

SCANNING BEAMS • Used with __ energies (above __ MeV) to reduce __ contamination. • 2 computer‐controlled __ deflect the beam across planes and "scans" the beam into a clinically useful field.

Higher, 25Mev, brems Magnets

Closer electron shells have the lowest/highest binding energy and the least/most potential energy

Highest Least

An indication of how homogeneous the beam is. Defined as the ratio of the first HVL to the 2nd HVL

Homogeneity Coefficient

Transmission Formula. Explain symbols

I = Io e ^-.693(x)/HVL I = final beam intensity I0 = initial beam intensity e = the base of natural log .693/hvl = linear attenuation coefficient x = thickness

When dealing with scientific notation, if you move the decimal to the right, does the exponent increase or decrease if the exponent is negative?

Increase

6 FFF pros 1.Increased/decreased dose rate = decreased treatment time = less patient motion 2.Reduced __ from treatment head 3.Reduced __ 4.Reduced "__ __ __" dose 5.Reduced __ contamination 6.Sharper __

Increase Leakage "Out of field" Neutron Penumbra

Depth of isodose curve increases with increased/decreased energy

Increased

INFLUENCING FACTORS OF GEOMETRIC PENUMBRA Source Size: Increase the source size = Increased/decreased penumbra. SSD: Increase the SSD = Increased/decreased penumbra. Depth in the patient where penumbra is of interest: Increase the depth = Increased/decreased penumbra. SDD or SCD: increase the SDD = Increased/decreased penumbra.

Increased Increased Increased Decreased

• As beam energy increases, depth of Dmax increases/decreases.*** • As field size increases, depth of Dmax increases/decreases.

Increases Increases

DEPTH DOSE OR PERCENT DEPTH DOSE • Beam Energy: As beam energy increase, PDD or DD increases/decreases. • Field Size: As field size increases, PDD or DD increases/decreases. • SSD: As SSD increases, PDD or DD increases/decreases. • Depth of Tumor: As tumor depth increases, PDD or DD increases/decreases.

Increases Increases Increases Decreases

First, a charged particle is created and released; • Second, the charged particle deposits energy through Coulomb interactions. Direct or indirect ionizing radiation?

Indirect

Wavelength & Energy have an direct/indirect relationship

Indirect

Wavelength & Frequency have an direct/indirect relationship

Indirect

: X-rays, Gamma Rays, Neutrons are direct/indirect ionizing radiation

Indirectly

Kerma is only applicable to direct/indirect ionizing radiation

Indirectly ionizing

Elastic or inelastic interaction? If the energy is not the same, some energy has been lost, then an inelastic interaction has occurred. The process starts the same but some of the energy of the electron is given up to the target. That electron is deflected from its original path but some of its energy has been transferred to an orbital electron or its been emitted in the form of a photon. the momentum (speed) is the same but the kinetic energy has changed. So __ scattering refers to any process that causes the primary electron to lose a detectable amount of energy. Part of that kinetic energy has changed to some other form of energy in that interaction

Inelastic

- Some kinetic energy is lost during the collision and reappears in another form of energy

Inelastic interactions

Collision Processes Produce Characteristic Radiation: •High speed electrons hit target and transfer some of momentum to the inner shell electrons in the target material ‐‐ called a collision process; a type of elastic/inelastic interaction •This ADDITION of energy ionizes the target atoms • Ionization causes a void in an inner orbital shell •An outer shell electron (in a higher energy state/shell) moves inward to fill the void; this requires the release of energy •Release of energy is in the form of Characteristic Radiation •Energy RELEASED in the form of characteristic radiation DEPENDS on what?

Inelastic. The difference of the binding energies of the involved orbital shells.

Geiger-Muller Detector Uses __ gases like helium, argon or neon Very sensitive; A single photon/particle can ionize all the inert gas atoms in the probe -Gas Multiplication aka __ __ __ alert when ionizing radiation is detected Indicator of radiation, not precise measurement. __ is when the device cannot function until polarization voltage is re-established -Quenching agents

Inert Townsend Avalanche Audio Dead time

Collision Interactions (Inelastic) •High speed electrons hit target and transfer some of their momentum to the electrons in the atoms of the target material. •Energy applied is enough to ionize target atoms • Ideally ejecting an inner/outer shell electron (__, __ shell).

Inner K, L

• Defined as the amount of radiation present per unit time per unit area perpendicular to the beam direction at point of interest

Intensity

Linear Attenuation Coefficient Affected by: Energy of the beam (Direct or inverse?) Electron density of the absorber (Direct or inverse?) - State of the absorber (gas/solid/liquid) Atomic number.....important with higher/ lower energies, less/more important with therapy energies (Direct or inverse?)

Inverse Direct Lower Less Direct

The intensity of a beam is inversely proportional to the square of the distance from the source. What law?

Inverse Square Law

Inverse Square Law The intensity of a beam is __ proportional to the __ of the distance from the source

Inversely Square

Proportional counters: Gas is ionized, then # of __ created is proportional to the energy of the particle

Ion pairs

For low voltage devices, the electrons may not even be collected because they're traveling so slow not enough voltage to accelerate these electrons. they will simply recombine with the gas.

Ion recombination

Ionization is the addition or removal of an electron from orbit

Ionization

3 kinds of gas-filled chambers?

Ionization Chamber Proportional Counter Geiger-Mueller Counter

Measure and monitor both electron and photon beam output • Monitors/samples the beam for its symmetry in the right/left and inferior/superior direction • Produces electrical signals that terminate the beam when the prescribed dose is given

Ionization chamber

What is the simplest gas filled chamber?

Ionization chamber

Has enough energy to remove tightly bound electrons from orbit of an atom causing the atom to become charged or ionized

Ionizing radiation

Electron Beams and Bolus: Uses include: • Flatten out or fill in an __ __ • Reduce __ to spare underlying tissue • Shape __ distributions to better conform to the treatment volume • Increase the __ dose Is skin sparing lost when a bolus is used? Partial bolus should not be used due to __ effect • Bolus can reduce dose, leading to a non‐ uniform dose if partial bolus is used. • Higher/lower dose in un‐bolused area, higher/lower dose in bolus area

Irregular surface Penetration isodose Surface Yes Edge Higher, lower

__ curves show depth dose. __% is dmax

Isodose curves show depth dose. 100% is dmax

Same atomic number and mass number, different arrangment

Isomer

: Same number of neutrons, different # of protons

Isotone

4 units of work and energy

Joule 1 J= 1Newton meter 1 J= 1 kg m2/s2 1.6 x 10(-19) J= 1 electron volt.

Do low voltage detectors read all ionizations or just the primary ones?

Just the primary ones, no secondary crap

Amount of energy transferred to electrons by incoming photons

KERMA

Absorbed Dose • The amount of energy from ionizing radiation absorbed in matter per unit mass of irradiated material at a specific point • In MeV energy ranges, kerma is greatest where? And absorbed dose is greater where?

Kerma is greatest on surface of skin Absorbed dose is greater below surface

Polychromatic = Polyenergetic = Heterogeneous Beam consists of a spectrum of photon energies Highest energy (peak energy) =peak __ applied to the tube Mean energy is 1/3‐1/2 of the peak Depends on filtration

Kilovoltage

Energy of Motion

Kinetic energy

The amount of energy anionizing particle transfers tothe material traversed perunit distance. (Expressed inkeV/μm)

LINEAR ENERGY TRANSFER (LET)

Importance of Radiation Quantities: Standard quantities or units help to: • Establish a common __ among professionals • Describe the amount of __ delivered • Allows for the prediction of __ __ and __ outcomes

Language Radiation Biologic effects and therapeutic

• Occurs with low percentage isodose lines • Isodose lines expand laterally with increased depth due to side scatter. • As electron energy increases, bulging decreases 2 names

Lateral Bulge or Ballooning

Occurs in high percentage isodose lines (90%) of beams 15MeV or higher • High isodose lines taper inward under the surface ("flowerpot effect") • Requires increase in margin (1cm) to assure coverage at depth.

Lateral Constriction

Equation for area

Length x width

Equation for volume

Length x width x height

SPECIAL CASES OF COMPTON Direct Hit: • Incoming photon has direct hit of atomic electron • Electron moves in same direction of incoming photon (0°) with most of the energy • Scattered photon will travel backwards (180°) with minimum energy of less than or equal to __MeV

Less than or equal to .255 Mev

Probability per unit thickness of a filter that any one photon will be attenuated

Linear Attenuation Coefficient

• Probability per unit thickness that any one photon will be attenuated

Linear Attenuation Coefficient (μ)

Average energy deposited per unit path length

Linear Energy Transfer (LET)

Linear Attenuation Coefficient Probability per unit thickness of a filter that any one photon will be attenuated Differs from attenuation coefficient because it is expressed in a __ or __ Expressed in a positive/negative value because it is the inverse of length (1/cm or cm‐1, 1/mm or mm‐1 ) Directly/inversely related to HVL

Linear dimension or length. Positive. Inversely

Thermoluminescent dosimeters A type of solid-state detector Detection Process: • Radiation interactions with *__ or __ crystals • All or part of photon's energy deposited in __ • Ionization occurs, free electrons result • Free electrons are "__" • When TLD is heated ,the captured electrons are released • Electrons release the energy as visible light when heated (called __). • Light is measured using a __ tube. • Light is proportional to the amount of __ deposited

Lithium fluoride or calcium fluoride crystal trapped Thermoluminescence Photomultiplier energy

DISADVANTAGES OF LOW ENERGY UNITS Low beam energy -Yields low penetration Little to no skin sparing -Yields high skin dose Low output or dose rate -Yields shorter/longer treatment times Large penumbra -Yields shorter/larger treatment fields Are dose profiles flat? -Yields less uniform distribution of dose Unable to use __ treatment techniques -Due to low output, treatment distances were short

Longer Larger NOT flat isocentric

6 cons of FFF 1.Shorter/longer treatment planning times 2.Ion chamber and EPID __ 3.Increased __ leakage 4.Increased/decreased risk with errors due rapid dose rate and high dose per pulse 5.Requires additional __ and routine __ 6.Measurement devices (like ionization chamber) are __ __ dependent

Longer Saturation Interleaf Increased commissioning, quality assurance Dose rate

How to remember the 4 atomic categories?

Look at the 2nd to last letter of each. Isomer= E PNAE: P=protons stay the same N: neutrons stay the same A=same atomic mass # e=everything stays the same

Characteristic Isodose Shape: Lateral Bulge or Ballooning • Occurs with high/low percentage isodose lines • Isodose lines expand laterally with increased depth due to side scatter. • As electron energy increases, bulging decreases Lateral Constriction • Occurs in high/low percentage isodose lines (90%) of beams __MeV or higher • High isodose lines taper inward under the surface ("flowerpot effect") • Requires increase in margin (__cm) to assure coverage at depth.

Low High, 15 MeV 1cm

Do high or low energy beams attenuate more

Low energy beams attenuate more. High energy beams just go through

Beam Direction Lower/higher energy results in more angular spread

Lower

Ionization chambers are where on the voltage scale

Lower end

Used for patient readings. only measures voltage before and after exposure to calculate dose

MOSFET

Difference between linear attenuation coefficient and Mass Attenuation Coefficient?

Mass Attenuation Coefficient removes the dependence on physical state of the absorber

Shifts dependence from nature of absorber to atomic structure • Example water vapor, ice, and liquid water = IT'S ALL WATER

Mass Attenuation Coefficient (μ/density)

4 Scintillation detector uses

Measure activity of radionuclides Discriminate one isotope from another Measure surface contamination Measure brachytherapy source leakage via wipe tests

The close the beam is to 1.0 homogeneity coefficient, the more mono or poly energetic the beam is?

Monoenergetic

Is pair production common

Nah

Is geometric penumbra effected by field size?

Nah, "Independent of field size"

What kind of radiation detectors are important in proton therapy and when energy of our photon s is greater than 10MV due to photodisintegration interactions.

Neutron detectors

Does any ionization happen in pair production?

No. The photons created could maybe ionize something but we're not talkin bout that

Does coherent scatter cause a biological effect?

Nope

Radiative Process Produces Bremsstrahlung Radiation • Involves an interaction between a high‐ speed electron and the __ of target atoms ‐‐ called radiative process; a type of elastic/inelastic interaction •The attraction between the negative electrons and positive nuclei causes the electrons to __, which requires the RELEASE of energy in the form of Bremsstrahlung or "__" radiation •Maximum energy of Bremsstrahlung radiation depends on the kinetic energy of the incoming electron (Ranges from 0 to Emax) • The greater the change in direction of the incoming electron, the higher the energy of the released photon

Nucleus Inelastic Slow down Braking

Energy of Characteristic Radiation Energy of the Characteristic photons will be equal to the difference of the binding energies between the involved orbital shells. __ ‐ __ = Energy of Characteristic Photon EXAMPLE: Find the energy of a characteristic photon which results from a transition between an outer orbital shell with a binding energy of ‐50KeV and an inner orbital shell with a binding energy of ‐85KeV.

Outer Shell BE ‐ Inner Shell BE 35 KeV

Which interaction? Incoming photon with at least 1.022MeV interacts with the electric field of an atomic nucleus As the photon approaches the nucleus of the atom, its energy changed into mass (in the form of a negatron and positron) Negatron eventually comes to rest Positron collides with a free electron (Pair Annihilation) Positron and free electron are destroyed and their energy is re-emitted as two .511MeV photons traveling 180° from each other (mass converted back to energy) This interaction is an example of the E=mc2 principle Energy converted to mass and then back to energy.

Pair Production

Comes from subatomic particles traveling at very high speeds most are directly ionizing.

Particulate radiation

where dose rate changes rapidly and the edge of the field is fuzzy and weird

Penumbra

PHOTONUCLEAR INTERACTION 2 other names

Photodisintegration or Gamma-n Interaction

COMBINED INTERACTIONS No single interaction occurs when radiation interacts with matter __ is predominant with radiation therapy imaging (kV) __ is the most predominant interaction in radiation therapy energy range. __ interactions occur when photon interact with our machine and stuff

Photoelectric Compton scatter Photonuclear reactions

When the incoming photon has an energy equal to or just SLIGHTLY GREATER than the binding energy of the inner orbital shell in which the electron is housed a LARGE INCREASE in __ occurs

Photoelectric absorption

Are photon beams or electron beams more predictable?

Photon

Electron/Photon Abutment If electron abuts at the surface with a photon field: ◦ Hot spot develops on the side of the photon/electron field ◦ Cold spot develops on the side of the photon/electron field ◦ This is due to the __ of the electrons from the electron field

Photon Electron Out-scattering

FIGURING POSITRON & NEGATRON ENERGIES Find the kinetic energy given to each particle if a 6MeV photon interacts via Pair Production (presume equal distribution).

Photon Energy - Threshold Energy = Available Energy 6MeV - 1.022MeV = 4.978MeV 4.978/2 = 2.489MeV Each particle receives 2.49MeV

Diode detectors A type of solid-state detector Measures dose or dose rate of __ & __ beams -Different __ used for photon vs. electron beams Uses are like TLD's: -Measuring dose at accessible __ -Measuring dose at patient surface sites -QA tool to assess flatness, symmetry, dose & dose rate -Can/cannot be used for absolute dosimetry Advantage: Gives instantaneous dose reading

Photon and electron diode organs Cannot

which interaction? High energy photon is absorbed by the nucleus of an atom Atom becomes radioactive & emits a neutron (or another nuclear particle)

Photonuclear interaction

what are the 6 degrees of freedom

Pitch, roll, and vertical

Cutie Pie Portable/stationary ionization chamber Serves as: • A __ for area surveys • A __ exposure instrument Used to measure: • Exposure rates around an __ patient. • Exposure rates around an __ patient's room. • Exposure rates in/around __ storage areas. • Cumulative exposures received outside protective barriers, such as around __ units.

Portable Rate meter Cumulative implanted implanted radioisotope treatment

Stored Energy

Potential energy

• Stores pulsed power supply used to accelerate electrons • Contains one‐way rectifiers that turns incoming alternating current to direct current

Primary Power Distribution System

ATOMIC MASS NUMBER: The number of nucleons (__ + __) in the nucleus

Protons + neutrons

Mass of all 3 subatomic particles

Protons and neutrons have a mass of 1 amu and electrons have a mass of 0 amu

COBALT CALIBRATION AND LEAKAGE • Who must perform full calibration testing? 4 instances when hould be performed? • When __ is replaced • If __% deviation is noticed during check • After a major __ is done • how often if none of these happened?

Qualified radiation physicist • When source is replaced • If 5% deviation is noticed during check • After a major repair is done • Monthly

• Energy distribution of photons in the beam (the spectrum) • Refers to penetrating ability

Quality

systematic quality analysis and review of patient care data.

Quality Assessment

- systematic monitoring of the quality and appropriateness of patient care with an emphasis on performance levels.

Quality Assurance (QA

series of activities or documentation performed with the goal of optimizing patient care.

Quality Assurance Program

a component of quality assurance used in reference to the mechanical and geometrical tests of radiation therapy equipment.

Quality Control (QC)

systems and processes used for decision making related to reliable functioning of continuous quality improvement, quality assurance, and quality control.

Quality Management (QM)

• Number of photons in the beam

Quantity

What are the 4 major standardized radiation quantities? What are their symbols?

READ Radioactivity (A) Exposure (X) Absorbed Dose (D) Dose Equivalent (H)

HT=Dose equivalent HT in rem = Dose in __ x QF HT in Sv = Dose in __ x QF • How to solve when Different radiation is considered?

Rad Gy HT = (D x QF)1 + (D x QF)2 + (D x QF)3

Energy in transit Travels as waves or in bundles called "photons" • Comes in many forms

Radiation therapy

Quality factor is aka

Radiation weighting factor (i know this from x-ray school)

Collision or radiative? ◦ Electrons interact with the Coulomb force of the absorber material nuclei ◦ Occurs with high Z material; Leads to Brems production ◦ High Z = More protons = Stronger Coulomb Force

Radiative

CO‐60 MONITORING & LIGHT SYSTEM • Light system to show when machine is on and off • If the beam is "on," a __ light must be lit • If the beam is "off," a __ light must be lit -In what 3 locations? • An __ Monitoring System is used to detect radiation in treatment room

Red Green • On console, head of the machine, and entrance to the room Area

Used in place of scattering foil • Used with higher energies (above 25MeV) to reduce Bremsstrahlung contamination. • 2 computer‐controlled magnets deflect the beam across planes and "scans" the beam into a clinically useful field.

SCANNING BEAMS

• Movable jaws that shape the beam in x and y directions to define a rectangular field.

SECONDARY COLLIMATOR

Equation for penumbra and what the symbols mean

SS x (SSD + d - SDD) / SDD SS = source size or focal spot size SSD = source to skin distance d = depth SDD = source‐to‐diaphragm distance or source‐to‐collimator distance Some texts write it as SS x {SAD ‐ SDD} / SDD

SUPERFICIAL UNIT Beam energy of __-__kV SSD of __-__cm Uses filters of what material? (__-__ mm thick) to harden the beam. Uses __ or __ to define a field sizes. Poor/rich depth dose At .5mm the dose is __% At 3cm the dose is already down to __%. __ __ is a key concern

SUPERFICIAL UNIT Beam energy of 40‐ 150kV SSD of 15‐20cm Uses filters of aluminum (1 - 6 mm thick) to harden the beam. Uses cones or applicators to define a field sizes. Poor depth dose At .5mm the dose is 90% At 3cm the dose is already down to 50%. Differential absorption is a key concern

Attenuation occurs by way of __, __ and __ (Inverse Square Law) Influenced by: Energy: higher energy = more penetrating = more/less attenuation Matter: higher density, atomic number, electrons per gram = more/less attenuation

Scatter and Divergence (Inverse Square Law) Less More

SPECIAL CASES OF COMPTON Grazing Hit: • Incoming photon has a grazing hit of atomic electron • Causes very little energy loss • Most of the energy is carried away by the __, which will have nearly the same energy as the incident photon

Scattered photon

5 kinds of solid state detectors?

Scintillation Detector Silicon Diode Diode Detector MOSFET Detector Thermoluminescent Dosimeter (TLD) Optical Stimulated Luminescence (OSL)

PROS & CONS OF G-M COUNTERS Pros Highly __ -Sensitive enough to detect individual particles Able to detect very high/low levels of ionizing radiation Cons Different energies may result in different responses: -Under-responds at very low/high energies -Over-responds at moderate/significant energies -Fails to respond at very low/high energies Dead time Cannot detect __ particles Limited __

Sensitive Low Low Moderate High Uncharged Life

Scattering Foil Used to __ the __ beam for clinical use. Thin sheet of high/low Z material in path of beam. __ contamination does occur. Scanning Beam __ beam is scanned by __fields which distributes the beam evenly throughout the field (widens it and makes it more uniform). Useful above what energy? More/less Bremsstrahlung contamination. which is most common and simple?

Simple Widen the electron beam High Bremsstrahlung Electron Magnetic 25 MeV Less Scattering foil is more common and simpler. Scanning beam is more complex.

5 PROS OF IONIZATION CHAMBERS

Simple/complex Accurate/Precise Possess a flat response -Responds similarly to all energy levels Effectively measures high levels of radiation No Dead Time

TLD USES Measurement of __ dose Measurement of dose at __ Measurement of dose __ Used as __ tool to assess flatness, symmetry, dose and dose rate Treatment field __ determinations __ monitoring Can/cannot be used for absolute dosimetry

Skin Field abutments Homogeneity QA Dose Personnel Cannot

Clinical Uses of electron beams: Treatment of __ cancers Treatment of breast cancers (__ scar boost, __ scar boost, IMN) __ treatment of large chest wall lesions Treatment of scar boost and __ Treatment of posterior __ nodes for traditional 3 field H&N Total skin irradiation for Mycosis __

Skin Lumpectomy, mastectomy Rotational Lymph node neck Mycosis fungoides

Early method of dose measurement• Used with early treatment units• Skin was a dose limiting structure• Defined as the amount of radiation to 'barely visibly' redden the skin of a light-skinned person

Skin Erythema Dose

An inherent characteristic of MeV beams Maximum dose or peak dose is delivered below the skin surface Skin no longer a dose limiting structure

Skin Sparing

Scintillation detectors A type of solid-state detector Most used scintillation crystal is __ More/less sensitive than G-M counters Emit __ (aka __) when irradiated -Converts energy of radiation into flash of light The amount of light produced is proportional to the energy of the photon absorbed by crystal -Higher energy photon = less/more light A __ tube (or photodiode) converts light pulse to an electric pulse Energy of the absorbed photon

Sodium iodide Much more sensitive Light aka luminescence More Photomultiplier

4 INFLUENCING FACTORS OF GEOMETRIC PENUMBRA

Source size SSD Depth in the pt where penumbra is being measured SDD or SCD

Proportional counters: Count radioactive __ Used as __ in some CT units Used in __ settings to detect __, __, and other low/high levels of radiation

Spills Detector laboratory alpha, beta high

Occurs as a result of ionization that's occurring in the stem body or the metal shielding rather than the actual point of measurement. (measuring ionizations of the metal itself also) (bad).

Stem effect

Fundamental force that. Binds protons and neutrons within an atom's nucleus (STRONGEST FORCE).

Strong interaction.

Natural force that • Hold protons and neutrons together

Strong nuclear

5 Possible gm counter uses

Survey of operating room, personnel, and instruments after implant procedures Find lost radioactive seeds or ribbons Monitor incoming radioactive source material packages. Search for holes in the walls of the linear accelerator room Use as an in-room radiation monitor for treatment room

CO‐60 unit EMERGENCY PROCEDURE alternative • Can Retract the source into the housing using a __ • It is __-__ inches in length • First 7 inches painted __ • Next 7 inches painted __ Push bar in there till you cant see any red color on the t-bar

T-bar 18-24 inchest Red Yellow

The smallest unit of an element that retains the property of that element

THE ATOM

What determines the function of a gas filled detector?

The amount of voltage applied to it

Gas filled chamber but it differs from parallel plate in that active volume of gas in housed within thimble shaped cavity and has interconductive surface (cathode) and a central anode. Just shaped differently.

Thimble ionization chamber

Traditional and SI unit of exposure

Traditional: roentgen (R) SI: Coulomb per kilogram (C/kg)

Accounts for beam that made it all the way through

Transmission

Equal absorbed doses of different types of radiation produce different amounts of biologic damage. True or false?

True

In the energy ranges of radiation therapy, kerma is greatest at the skin surface and absorbed dose is greatest below the skin surface. True or False

True

Newton's Laws of Motions: An object remains at rest, and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an __ force. The acceleration of an object depends on the __ of the object and the amount of __ applied. Whenever one object exerts a force on another object, the second object exerts an __ and __ on the first

Unbalanced Mass, force Equal and opposite

Electron density goes up = Linear Attenuation Coefficient goes up/down

Up

When atomic number goes up, change of pair production goes up or down?

Up

Number of electrons in the outer most orbital shell • Determines the chemical activity of an element

VALENCE

What causes ions to move to oppositely charged electrodes so they can be measured in a gas filled detector?

Variable voltage source and the 2 electrodes

Are polychromatic beams attenuated at the same rate or varying rates?

Varying rates, come photons might not even be attenuated at all

Which method for correcting output due to extended distance uses a virtual ssd, not an effective ssd?

Virtual Source Method

OMPONENTS OF A GASFILLED DETECTOR Variable __ source Gas-filled counting __ Two __ well insulated from each other Ion-pairs: Produced by radiation in fill gas Move under influence of __ field Produce measurable current on electrodes, or transformed into pulse

Voltage Chamber Electrodes Electric

Electromagnetic radiation can act like or have characteristics of a wave or a particle • EMR particle can also be thought of as a bundle of energy known as "photon". What is this theory called?

WAVE-PARTICLE DUALITY THEORY

Fundamental force that is Responsible for the decay of unstable (radioactive) elements

Weak interaction.

SAFETY TERMS __- The prescription. Must be clear and signed by the licensed "authorized user" __‐ Failure to complete a planned action as intended or the use of an incorrect plan of action to achieve a given aim __‐ An unwanted or unexpected change from a normal system behavior which causes or has the potential to cause an adverse effect to persons or equipment __‐ An event or situation that could have resulted in an accident, injury, or illness but did not either by chance or through timely intervention. Also known as a close call, good catch --"Radiation therapists should be encouraged to report both errors and near‐misses." (ASTRO) __-Use of standardized approach to help review the most crucial aspects of a radiation treatment delivery process 6

Written directive Error Incident Near-miss Time-out

2 kinds of electromagnetic radiation

X-ray and gamma rays

What are the 3 forms of low let radiation

X-rays • Gamma Rays • Beta Particles (Electrons)

Equation for exposure rate

X/t or exposure/time

Do particulate radiation have a mass?

Yes

Directly Ionizing Radiation: Has a charge or no? Deposits energy through direct __ interactions

Yes has a charge Coulomb

Temperature and pressure correction factor equation

[(T+273)/295) x (760 / P)] T= Temperature in Celsius P = Pressure

2 parts of the carousel

a) Flattening Filter b) Scattering Foil or Scanning Beam

the measurement of a quantity with an instrument of the highest metrological quality

absolute dosimetry

fMedium Factor depends on what 2 things

affective atomic # and type of radiation

THE ATOM The smallest unit of an element that retains the property of that element • The mass of an atom is measured in what 3 things? • __ Law: every gram atomic weight of a substance contains the same number of atoms • __ Number = __ atoms per gram atomic weight

atomic mass unit , atomic weight, or gram atomic weight Avogodro's Avogodro's number=6.0228 x 10^23 atoms per gram atomic weight

ATOMIC NUMBER: The number of __ in the nucleus

atomic number

NEUTRON DOSIMETERS: Chamber coated with __ or filled with __ or __ gas -For fast neutrons, the device is surrounded by a moderator made of __ material to slow neutrons down Neutron interaction with device causes a __ reaction The energetic charged particles produced in the reaction will ionize __ and create products that are measured Operate in the __ region

boronor filled with boron tri-fluoride or helium-3 gas. hydrogenous Neutron-alpha Gas atoms Proportional

FLATTENING FILTER Located on the __ --Today, some equipment is flattening filter free • Made of what 4 materials? • Used only when programming electron/photon beams • Makes the photon/electron beam more uniform at depth --Attenuates radiation more at the __ of the beam --Causes __ peripherally to make beam more useful • Proper alignment is essential or the beam uniformity hitting the patient will be impacted

carousel lead, steel, cooper, brass photon photon Center Scatter

Scattering foil: Located on the __ • Used only when programming photon/electron beams • Makes photon/electron beam more clinically useful • Spreads out the small, pencil‐ like beam of photons/electrons and provides a flat, uniform electron treatment field • Made of thin sheets of high/low Z material. 2 examples?

carousel Electron Electron Electrons High, copper or lead

Units for Mass Attenuation Coefficient

cm^2/g

Virtual Source Method: D'max = Dmax(SSDvir + dmax)2 / fair(SSDvir +g_ dmax)2 Uses virtual SSD, as opposed to effective SSD Fair accounts for the variation in the inverse square law for small field sizes, low beam energy, and large air gaps ◦ Depends on what 3 things

energy field size extent of air gap

DEPTH DOSE OR PERCENT DEPTH DOSE A measure of beam __ and __ • This ratio describes relative dose of radiation at any depth • Equation? • Given as a __ (percent depth dose) or __ (depth dose) • 4 Influencing Factors?

energy and penetration Dose at depth / dose at Dmax percent or fraction Beam energy, field size, ssd, and depth of tumor

Internal shielding for electron beams: Internal lead shields may be used to block areas such as the 4 examples? ◦ The use of lead shielding would cause a very high level of __ ◦ The highest dose is where the lead shield meets the tissue; called the lead‐tissue interface-Dose can be __-__% greater. Low atomic number coating material is placed between the shield and the tissue to absorb electron backscatter. 2 examples?

eye, lip, nostril or cheek backscatter 30-70% paraffin wax or dental acrylic

Used to relate exposure in air to dose in medium • Is a function of composition of medium and photon energy

fMedium Factor

the agent that makes a change in motion

force

Beam hardening Applies to mono/heterogeneous photon beams only A filter will absorb a greater fraction of lower energy photons; causes the average energy of the beam to increase/decrease?

heterogeneous INCREASE

Homogeneity Coefficient: An indication of how __ the beam is. Defined as the ratio of the first __ to the 2nd __. Homogeneity Coefficient = __ / __. Every HVL of mono‐energetic beams is the same/different thickness. HVL for poly‐energetic beams increases/decrease from the 1st HVL to 3rd HVL due to beam hardening.

homogeneous HVL HVL 1st HVL / 2nd HVL Same Increases

Study practice problems in journal

ight

PROPORTIONAL COUNTERS: Perform similarly to a __ Due to operation __, can result in gas multiplication (like GM-Counters) Discriminate between what 3 radiations? Suitable for measurement of low/high intensity radiation Produces a __ proportional to the radiation energy absorbed during the ionizing event

ionization chamber. voltage alpha, beta, and gamma radiation low pulse

IONIZATION (ION) CHAMBER Consists of: Gas-filled chamber, or probe Electrical charge applied to it across two electrodes Detection Process: Chamber exposed to radiation Air is ionized Ion pairs move to oppositely charged electrodes Movement of __ creates an electrical current __ amplified and displayed on a meter Used to: Calibrate __ or Co-60 units (absolute dosimetry) Measure treatment __ characteristics Used in linear accelerator monitor chambers

ions Current Linear accelerators beam

ATOMIC CATEGORIES: Same number of protons, different mass number

isotope

Thoraeus filter was used in what two kinds of units? It consists of what 3 layers in order from closest to target to closest to patient. Highest atomic number # is highest next to the target/patient.

kilovoltage and orthovoltage Tin, copper, and aluminum. Highest atomic # is closest to target

What does KERMA stand for?

kinetic energy released in matter

Force equation

mass x acceleration

anything that has mass and takes up space

matter

HalfValue Layer(HVL) A specific thickness of material that reduces the beam intensity to exactly half of its original intensity. Expressed in what two units? HVL can be an indicator of beam quality (energy) for mono or poly chromatic beams? Higher HVL = lower/higher energy beam = lower/higher attenuation coefficient

mm or cm Both Higher Lower

Transmission Formula: Used for mono/polyenergetic beams

mono

The number that differntiates high LET radiation vs low

more than 10 keV/μm is high LET. Less than that number is low

What are the 4 forms of radiation?

non-ionizing and ionizing Particulate Electromagnetic

The __ Rule = no more than 8 electrons can be in the valence orbital shell

octet

Intensity Depends on what?

quality and quantity

what does rad stand for

radiation absorbed dose

MEDICAL ACCELERATOR SAFETY CONSIDERATIONS Emergency Procedures: --Written polices should be at or near __ --Radiation therapists should be familiar with policies --Knowing location of __ buttons is critical. __: --Serves to evaluate near misses, events, and procedural issues that could lead to errors Multidisciplinary Case Conferences or Tumor Boards: --Review and evaluation of patient cases for optimal coordination of patients care __ Events: --Incorrect application or delivery of prescribed dose

treatment control console emergency stop review committee medical events

ELEKTA - SLALOM BENDING MAGNET • __ magnet system • Total bending of __ degrees • __ degree bend toward patient

triplet 202.5 112.5

WHAT IS RADIATION? Energy in transit • Travels as __ or in bundles called "__" • Comes in many forms

waves or in bundles called photons

All radiation detection devices must be easy to carry, operate, durable, reliable, interact w radiation similar to human tissue, detect common types of radiation and energy of radiation should not significantly affect the response of the detector. shouldnt change direction of radiation

ya

Percent depth dose is just saying that 70% of the dose is here, 60% is here, etc. The percent depth doses will be higher in higher energy beams at certain depths compared to lower energy beams at the same depth

ya

TREATMENT CONSOLE • Equipment used to control or operate the linear accelerator --Used to require manual input of MU, beam energy, wedge, field size etc. by the therapist --Now computer driven with data input from treatment planning system • Monitoring of patient from the console --Aural communication (speak to and hear the patient) --Indirect visualization (TV monitors) • Interlock system --Designed to protect patient & staff from hazards or unsafe use of the linear accelerator --Patient‐protection interlocks, beam energy, beam symmetry, dose, radiation, and mechanical hazards • Emergency off buttons --Terminates all electrical power to the equipment

ya

What is the HVL to Linear Attenuation Coefficient equation? What is the Linear Attenuation Coefficient to HVL equation?

μ= .693 / HVL HVL = .693 / μ

Exposure (X) Conversion Factors: • 1 R = __ C/kg • 1C/kg = __ R • 1 air kerma = __R

• 1 R = 2.58 x 10-4 C/kg • 1C/kg = 3876 R • 1 air kerma = 100R1

CO‐60 unit EMERGENCY PROCEDURES 2 steps if console timer fails to terminate exposure? What to do if source drawer fails to close by shutting off electrical circuits (actions above)?

• Activate emergency off button • Turn circuit breaker to off position • Open treatment room door • Remove patient from room • If ambulatory, ask patient to exit the room. • If non‐ambulatory or cannot respond to verbal commands, enter room, quickly remove patient while avoiding primary beam. • Close treatment door • Notify physician and RSO • Secure room • Note time

6 parts of gantry head

• Bending Magnet • Target (photon only) • Primary Collimator • Carousel • Ion Chamber • Jaws/MLC

3 examples of linacs with FFF

• CyberKnife • Tomotherapy • Varian True Beam

3 parts of gantry

• Electron Gun • Accelerator Structure • Gantry Head

Tissue Inhomogeneities Dose distribution of an electron beam is affected by: • __ density of material • Tissue __ variations • Tissue __ variations Example: Electrons travel further in lung than in bone • Electrons traveling through lung tissue would deliver a higher/lower dose to tissues beyond the lung (__-__%) • Tissue lateral to bone, may receive higher/lower doses due to scattering • Tissue beyond bone may be overdosed/underdosed (__%)

• Electron density of material • Tissue contour variations • Tissue type variations 15-35% Scattering 20%

ELECTRONS Do they have a charge? Do they have a mass? Are they directly or indirectly ionizing? • Have a maximum range in matter dependent on __ • Rapid dose fall off after __% dose level • Gives a high skin dose (__% +) • Used for __ skin lesions or __ tumors • The __-__, __ moves in place • Tissue __ have significant impact

• Have charge and mass (directly ionizing) Energy 90% 80% Superficial, shallow target & flattening filter retract, scattering foil in place. inhomogeneities

Same mass number, different atomic number

• Isobar

4 parts of drive stand

• Magnetron/Klystron • Waveguide • Circulator • Cooling System

PHOTONS Do they have a charge? Do they have a mass? Are they directly or indirectly ionizing? • Exponentially/barely attenuated by matter • Gradual dose fall off after __ • Offers more/less skin sparing • Used to treat deep/shallow seated tumors • The target & __ are in place • Tissue inhomogeneities have more/less impact than for electron beams

• No charge, no mass (indirectly ionizing) Exponentially Dmax More Deep flattening filter less

what are the 2 cons of tld

• No permanent record • Not an instant reading

- the totality of features and characteristics of a radiation therapy process to satisfy stated or implied needs of the patient.

• Quality

Limitations of Exposure (X) Only applicable to: • What kinds of beams? • Photons of __ energy or below • Counts products of __ (__), not a measure of absorbed energy or actual photons

• X-ray and gamma ray photons • 3MeV or below • Counts products of ionization (ions), not a measure of absorbed energy or actual photons

EMR spectrum from highest energy to least

• X-rays • Gamma Rays • UV light • Infrared • Radar • TV • Radio

Modifies and shapes isodose distribution, replaces physical wedges

•Dynamic Wedging

Delivers non‐uniform exposure across the BEV

•Intensity Modulated Radiation Therapy (IMRT)

Amplifies microwave power from a radiofrequency drive to accelerate electrons. (Best for energies >10MeV)

•Klystron

Tube that directs microwave power to the accelerator tube

•Waveguide

What 5 things are needed to calculate Electron beam MU?

◦ Tumor dose: Given in the prescription ◦ Prescribed isodose (DD): Given in prescription ◦ Machine Calibration Factor (Ccal): Standard for unit ◦ Cone/Field Size Output Factor (Cfs): Depends on cone size/extent of blocking ◦ SSD: Only matters if it is not 100cm

Equation relating wavelength and frequency. What do the symbols mean?

𝐶 = 𝜆c C=speed of light or 3x10^8 m/s 𝜆=Wavelength (measured in m) v=frequency (measured in Hz)