RT physics 1

Beta-minus decay occurs when....

N/Z is high

Given a generic chemical symbol....

N=A-Z

What are the three elementary particles found in an atom?

Neutrons, protons, and electrons

The ratio of dose at depth to dose at a reference depth is...

PDD

Which of the following are correct? At equal depths and field sizes the PDD for a 6 MV beam is greater than a 10 MV beam, the PDD decreases with increasing SSD, PDD decreases with increasing depth, the PDD will be greater for a 20x20 field size than a 15x15 field size

PDD decreases with increasing depth, the PDD will be greater for a 20x20 field size than a 15x15 field size

Which of the following is correct? Pair production needs a min of 1.02 mev to occur, as energy increases the prob of Compton effect increases, as atomic number increases the prob of Compton effect increases, in reference to Compton the max energy of a phton scattered at a 90 degree angle is .255 mev

Pair production needs a min of 1.02 mev to occur, as energy increases the prob of Compton effect increases,

Which of the following represents the ratio of the absorbed dose at any depth d to the absorbed dose at a reference depth.

Percent depth dose (PDD)

In which two interactions does the incoming incident photon lose all of it's energy?

Photoelectric and pair production

The process in which a photon interacts with an atom, ejects an orbital electron and all of the energy of the photon is transferred to the electron is called?

Photoelectric effect.

Which of the following is an ex of indirectly ionizing radiation?

Photons

The photons used in PET imaging are created by....

Positron emission

The number of which atomic particle determines the identity of an atom?

Proton

Which of the following are examples of directly ionizing?

Protons, electrons, and alpha particles

a process in which a nucleus with excess energy emits radiation to get rid of its excess energy &&& occurs because an unstable nucleus is trying to reach a more stable state.

Radioactivity

A farmer chamber is a measuring device used in radiation oncology for calibration of RT beams.

TRUE

A plot of optical density vs dose is called an H & D curve.

TRUE

Absorbed dose includes all radiation, all materials, and all energies.

TRUE

An increase in energy equals an increase in TMR.

TRUE

BSF (backscatter factor) = TAR a d-max.

TRUE

Characteristic x-rays are produced when electrons in an atom drop from one shell to the next.

TRUE

Diodes can be placed on a patients skin surface to measure dose received to that location during a particular treatment.

TRUE

Electromagnetic radiation travels at the speed of light.

TRUE

Electrons can be accelerated with electric and magnetic fields.

TRUE

Exposure is only defined in air.

TRUE

HVL is dependent on material and energy of the beam.

TRUE

In radiation therapy beams, electrons are used to produce photons.

TRUE

In reference to PDD, the dose at the normalization point is 100% and the dose to all other depths are expressed as a percentage of the dose at the reference depth.

TRUE

In stable elements the ratio of N & Z is even or 1:1.

TRUE

Kerma reaches its max at a depth of zero and decreases with depth.

TRUE

Klystrons amplify microwaves and are used in high powered linear accelerators.

TRUE

Linear accelerator is the name of the charged particle accelerator used in RT.

TRUE

Magnetrons produce microwaves and are used in low-powered linear acc.

TRUE

Masses of atoms and atomic particles are given in terms of atomic mass units.

TRUE

Megavoltage beams are hardened by inherent filtration in the target, as well as, in the flattening filter and therefore do not require any additional filtration.

TRUE

Percent depth dose is used in SSD monitor unit calculations.

TRUE

Secular equilibrium occurs when the half-life of the parent is much longer than the half-life of the daughter.

TRUE

Task group report 51 (TG-51) is a protocol physicist use to calibrate linear accelerators.

TRUE

The Bragg-Gray theory is the relationship between the dose in an ion chamber to the dose in the material surrounding the ion chamber.

TRUE

The Tissue max ratio is used instead of the tissue air ratio for megavoltage beams bc as energy increases the dose in free space becomes difficult to measure.

TRUE

The binding energy in a atom is the amount of energy needed to break apart the nucleus.

TRUE

The depth dose along the central axis of the beam is essential for calculating dose in the patient.

TRUE

The energy of photons produced by Bremsstrahlung is a continuous spectrum up to the energy of the incident electron.

TRUE

The energy of the x-ray given off during characteristic x-ray production is equal to the difference in the energy levels of the electrons shells.

TRUE

The highest dose for a single field 18 MV beam will be at 3 cm depth.

TRUE

The linear attenuation coefficient is a function of the material and the energy of the beam.

TRUE

The most common crystal used in TLD's is lithium fluoride.

TRUE

Thimble chambers measure exposure and are small and practical.

TRUE

Thimble chambers require electron equilibrium.

TRUE

Tissue maximum ratio (TMR) is used in SAD monitor unit calculations.

TRUE

Van de Graaff generators, betatrons, and linear acc are all examples of megavoltage x-ray machines.

TRUE

Which of the following statements regarding radiation exposure is/are correct? The Roentgen is a unit of exposure, 1 R= 2.58 x 10^-4 C/kg, and exposure is only defined in air, the roentgen is only applicable at photon energies above 3 MeV

The Roentgen is a unit of exposure, 1 R= 2.58 x 10^-4 C/kg, and exposure is only defined in air

The definition of an electron volt is?

The kinetic energy of a single electron accelerated through a potential difference (voltage) of 1 volt.

What is the proper order of a thoreus filter?

Tin, copper, aluminum

Which of the following represents the ratio of the dose at a point in a phantom to the dose in free space at the same point?

Tissue air ratio (TAR)

Which of the following represents the ratio of dose at a given point in a phantom to the dose at the same point at depth of max in the phantom.

Tissue max ratio

Which of the following statements regarding free air ionization chambers are correct? They can only measure energies above 3 MeV, they are routinely used in clinical setting, electronic equilibrium is fundamental to the measurement of rad exposure and is employed in the free air ionization chamber, they are used as a standard for other measuring devices to be calibrated against

electronic equilibrium is fundamental to the measurement of rad exposure and is employed in the free air ionization chamber, they are used as a standard for other measuring devices to be calibrated against

Megavoltage units =

greater than 1000 kV

Grenz-Ray units =

less than 20 kV

The quality of megavoltage x-ray beams is specified by...

maximum energy

Which of the following regarding free air ionization chambers is/are correct? They are routinely used in a clinical setting, they are used as a standard for other measuring instruments to be calibrated against, they can only be used to measure energies up to 3 MeV, electron equilibrium is fundamental to the measurements of radiation exposure and is employed in the free air ionization chamber

they are used as a standard for other measuring instruments to be calibrated against, they can only be used to measure energies up to 3 MeV, electron equilibrium is fundamental to the measurements of radiation exposure and is employed in the free air ionization chamber

Which of the following statements is not correct? The cathode and electrons repel each other, the tungsten filament is where electrons are created, the anode is positive and houses the target,

tungsten is a low Z material and has a high melting point

A patient is being treated with a field size of 5x5. The doctor decides to change the field size to 8x8. What happens to the %DD?

%DD increases

Define the decay constant for Cesium 137?

.02295 (.693/u)

Which of the following is the rest mass of an electron?

.511 MeV

Cal the temp/pressure correction factor if the current temp is 25 C and the current pressure is 755 mm HG.

1.0169

Pair production need a min of ____ to occur.

1.02 MeV

Positron emission requires...

1.02 MeV

It is desired that a 50% transmission block be constructed from cerrobend for a 6 MV xray beam. How many cm of cerrobend are needed?

1.6

1 ev =

1.602 x 10^-19

It is desired that a 50% transmission block be constructed from cerrobend for a 10 MV xray beam. How many cm of cerrobend are needed?

1.7

A 6 MeV beam is incident on a lead sheet 2.5 cm thick. If the initial dose rate of the beam is 350 cGy/min, what will the dose rte be after passing through the lead sheet if the linear atten coef for this beam in lead is .4911 cm^-1?

102.53 cGY/min

What percentage of dose transmission would result from 3 HVL?

12.5%

You are treating a patient who requires a 12 x 20 field size for treatment. What field size would you reference on your PDD chart?

15 x15 (similar squares formula)

Pd-103.

17 days

Iodine-125 is used for prostate seed implants. If the original activity was 30 mCi, what is the activity after 36 days.

19.66 mCi.

Calculate the annual rate of decay for Cs-137...

2.3%

1 dps =

2.7 x 10^-11

A sample of an isotope has a half-life of 74 days and is measured to have an activity of 6.988 Ci at 8am on that day. What will be the activity of the isotope 100 days later at noon?

2.735 Ci.

Orthovoltage therapy units =

200-350 kV

Calculate the mean life of Pd-103.

24.48 days.

A Co-60 beam has an intensity of 5000 photons/sec. After transversing 5 cm of water, the photon beam intensity is 1298 photons/sec. What is the percent transmission?

26%

Calculate the activity of a 35 mCi Cs-137 source after 12 years of decay.

26.57 mCi

The intensity of a radioactive beam is measured at a distance of 105 cm and found to be 250 mR/min. What will the intensity of this beam be at 100cm?

276 mR/min

The value of the speed of light is..

3.0 x 10^8 m/sec

What is the activity of a radioactive material after 5 half-lives?

3.125%

1 Ci =

3.7 x 10^10 bq

Cs-137

30.17 yr.

A 20 cm patient is being treated to mid-plane. A 2.5mm source is being used. The SSD is 100cm and the SCD is 40 cm. What is the geometric penumbra at mid-plane?

4.38 mm

A 18 MV beam has a focal spot (source diameter) of 4mm. What is the geo penumbra at a depth of 12 cm? The SSD is 100cm & SCD is 50 cm.

4.96mm

Contact therapy units =

40-50 kV

Co-60

5.26 years.

Orthovoltage therapy units routinely use an SSD of...

50 cm

Superficial therapy units =

50-150 kV

5.4 Gy equals??

540 cGy

What is the activity of a 6000 Ci Co-60 source after 6 months?

5616.8

I-125

59 days.

What is the max range and the 90% isodose level for a 15 mev beam?

7.5 cm max range and 3.75 cm for 90% (max divide by 2, 90% divide by 4, 80% divide by 3)

The min thickness of cerrobend required for a full thickness block for a 6 MV beam is....

7.65

For a 6 MV beam, the PDD for a 15x15 field size, 10 cm depth, 100cm SSD is 72.3%. Find the PDD for the same field size and depth for 105 cm SSD.

72.8%

Ir-192

73.83 days

The activity of a Co-60 source is 6.85 Ci today. What was the activity when the source was calibrated 462 days ago?

8.09 Ci

How many cm of cerrobend would provide a full thickness block for a 6 MV beam?

8.5 cm

Calculate the mean life of I-125.

84.96 days.

When treating a neck tumor at a depth of 2cm, which electron energy would provide adequate dose (90%) while sparing the spinal cord locate at 6 cm?

9 Mev

1 amu =

931 MeV

an isotope teletherapy unit first used in the 1950's, have a 5mm d-max, and average energy of 1.25 MeV

A Co-60 unit

Which formula represents the relation between original activity and current activity?

A=Aoe^-yt

The term "ionizing radiation" encompasses... directly ionizing charged particles, indirectly charged particles, electromagnetic photons

All

Which are correct? Proton therapy use beam energies in the 200 Mev range, an adv of treating with protons is the dose distribution with depth bragg peak is the region of high dose at the end of the particle range, and the types of accelerators used for proton therapy include linear acc, cyclotron, and synchrotrons

All

Which of the following are methods of artificially producing radionuclides? Alpha bombardment, neutron bombardment, and proton bombardment

All

Which of the following is correct? as radiation enters a material there is a dose buildup to max (d-max) due to secondary electrons, extrapolation chambers are used to measure surface dose, parallel plate chambers can be used to measure the dose buildup region, ionization chamber readings may need correction for several factors including temp and pressure

All

Which of the following is/are correct? Most modern linear acc can deliver beams up to 40x40 cm, linear acc use a flattening filter to make the beam intensity uniform across the whole beam, use a bending magnet to change the direction of the accelerated electron beam from horizontal to vertical

All

Which of the following regarding Kerma is/are correct? the unit of kerma is the same as dose (J/kg) or Gray (Gy), kerma is the highest at a depth of zero, after dmax, dose decreases at the same rate as Kerma, kerma is a measure of kinetic energy released when radiation interacts with a material.

All

Which of the following regarding roentgen to rad conversion factor is/are correct? The roentgen to rad conversion factor is also known as the f factor, the f factor lets you convert exposure into absorbed dose

All

Which of the following regarding scintillation detectors is/are correct? scintillation detectors can measure the energy spectrum of a photon beam, they have crystals that emit light when irradiated, the light emitted can be collected and converted to an electrical signal, the electrical signal is proportional to the energy of the original photon

All

Which of the following regarding thimble chambers are correct? require electron equilibrium, have air equivalent walls, measure exposure and are small and practical, farmer chamber is a type of thimble chamber used in rad oncology for calibration of radation therapy beams

All

Which of the following statements regarding photon interactions is/are correct? Compton interaction is the primary interaction occurring in energies between 30 KeV and 30 MeV, Pair production needs a min of 1.02 MeV to occur, and the max energy of a photon scattered at 90 degrees is 511 KeV and at 180 degrees is 255 KeV.

All

Which regarding LET is/are correct? LET is a measure of the energy transferred to a media as it is transversed by radiation, alpha radiation has a very high LET, and photon radiation has a very low LET.

All

Which regarding shielding is/are correct? HVL is the thickness of an absorber required to attenuate a radiation beam to half of its original intensity, full thickness blocks allow no more than 5% transmission of the primary beam, a 50% transmission block would require one HVL, 1 cm Pb=1.2cm of cerrobend

All

Which of the following statements are not correct. Alpha is very heavy, an alpha particle has 2 neutrons and 2 protons, is always positive, alpha can be positive or negative

Alpha can be positive or negative

Which of the following statements is not correct? As tube current increases, x-ray output decreases, as tube voltage increases, xray output increases, filament current affects tube current, a small change in tube current creates a large change in exposure rate

As tube current increases, x-ray output decreases

Every gram atomic weight of a substance contains the same number of atoms.

Avagodro's law

Name the mode of decay of Co-60.

Beta decay

Why is cerrobend preferred over lead?

Cerrobend cools quicker

This interaction occurs when the energy of the incident photon is much greater than the binding energy of the electron.

Compton effect.

Which photon interaction is most predominant in radiation therapy?

Compton effect.

Which equation describes the equivalence of mass and energy?

E=mc^2

Adding filtration to the x-ray beam decreases the penetrating power of the beam.

FALSE

As increase in field size equals a decrease in TMR.

FALSE

Calorimetry is the measurement of absorbed dose by measuring chemical changes.

FALSE

In Compton effect, the binding energy of the electron is much greater than the energy of the incident electron.

FALSE

Increasing beam energy decreases the skin sparing effect.

FALSE

The primary component of cerrobend is lead.

FALSE

Thimble chambers have water equivalent walls.

FALSE

X-ray tubes using half-wave rectification produce a higher output than full-wave rectification.

FALSE

X-rays, gamma rays, and electrons are examples of non-ionizing radiation.

FALSE

Transient equilibrium occurs when the half-life of the parent is much longer than the half-life of the daughter.

FALSE - much less

One bq is larger than one Ci.

FALSE --- 1 curie = 3.7 x 10^10 bq

As energy increases, the prob of PE absorption increases by E^3.

FALSE --- Z^3

Ionization is what happens when a photon interacts with an atom and moves an electron to a higher energy state.

FALSE --- excitation

As atomic number increases, the prob of Compton effect increases.

FALSE --- not Z dependent

1 cm of Pb = 2.1 cm of cerrobend.

FALSE -1.2

Characteristic x-rays are the result of an interaction between a high speed electron and a nucleus.

FALSE -brems

As atomic number increases, the prob of pair production decreases with Z^2.

FALSE -increases

The splitting of high atomic number nuclei, when certain high Z nuclei are bombarded with neutrons they capture those neutrons and split. The result is 2 smaller nuclei, neutrons, and gamma rays. Energy is given off in this process.

Fission

The combo of low atomic number nuclei to form a larger nucleus. Energy is given off in this process.

Fusion

The best material for shielding neutrons is...

Hydrogenous material

Which of the following regarding shielding is correct? If you increase the energy of the beam, the thickness of the HVL needed increases, a 50% transmission block would require one HVL, a full thickness block requires 4.5-5 HVL's, a full thickness block allows no more than 10% transmission of the primary beam

If you increase the energy of the beam, the thickness of the HVL needed increases, a 50% transmission block would require one HVL, a full thickness block requires 4.5-5 HVL's

The process by which a neutral atom requires a positive or negative charge is...

Ionization

- same mass number, different number of protons and neutrons

Isobars

- same number of neutrons, different number of protons and therefore diff mass number.

Isotones

same number of protons, different number of neutrons. Different mass number.

Isotope -

What is the SI unit of energy?

Joule