RT Physics 2 Final Prep
When selecting ovoids for a tandem and ovoid application, the optimal choice is the _____ diameter, since this will _______. Largest, spare the vaginal mucosa Largest, shorten the treatment time Smallest, cause the least discomfort to the patient Smallest, reduce the bladder dose Smallest, spare the vaginal mucosa
Largest, spare the vaginal mucosa
Sharp Irregularities in the path of a high energy electron beam results in: Increased Bremsstrahlung production Localized hot and cold spots in the underlying medium due to scatter Negligible changes in the dose distribution in the underlying medium None of the statements are true
Localized hot and cold sport in the underlying medium due to scatter
A TomoTherapy® unit incorporates which modalities into a single machine? Kilovoltage CT, proton accelerator Kilovoltage CT, megavoltage linear accelerator Megavoltage CT, megavoltage linear accelerator PET scanner, megavoltage linear accelerator MRI scanner, megavoltage linear accelerator
Megavoltage CT, megavoltage linear accelerator
Which of the following statement about N^{Q} /{D,w} is NOT correct? N^{Q} /{D,w} is a calibration factor based on the absorbed dose to water for a beam quality Q N^{Q} /{D,w} can be calculated by multiplying N^{60Co} /{D,w} and a beam quality factor kQ N^{Q} /{D,w} usually has a unit of Gy/C N^{Q} /{D,w} is established/provided by ADCLs every two years for all beam energies in the clinic
N^{Q} /{D,w} is established/provided by ADCLs every two years for all beam energies in the clinic
Which of the following statements below are correct regarding the Virtual Source Distance (VSD): The Virtual Source Distance (VSD) for a therapeutic electron beam: Is always 100 cm Is never used in clinical applications Needs to be determined for every energy and every electron applicator
Needs to be determined for every energy and every electron applicator
An H-D curve is a plot of: Absorbed dose vs. depth in tissue Incident vs. transmitted light intensity Net optical density vs. photon energy % surviving cells vs. absorbed dose Net optical density vs. log of absorbed dose
Net optical density vs. log of absorbed dose
IMRT Optimization algorithms use a/an _____________ to determine how close a plan is to meeting the goals stated by the planning team. Polynomial Function Objective Function Montonic Function Inverse Function Composite Function
Objective Function
In a clinic, the photon beam output for 6MV is initially calibrated at 1cGy/MU for 10x10 cm2 field size, 100 SSD at depth of dmax =1.5 cm. However, during an annual calibration, a physicist mis-calibrated this 6MV photon beam to be 1cGy/MU at 10cm depth, instead of dmax (SSD=100cm, field size 10x10 cm2). We know that %dd(10)=66.7% for this 6MV beam. What would be the effect on future patients? Overdosing by 33% None of the answers provided are correct Underdosing by 50 % Overdosing by 50% Underdosing by 30 %
Overdosing by 50%
When treating a small lung lesion which moves with respiration, which of the following techniques can be used without a gating system, a 4D CT or spirometer? Deep inspiration breath hold (DIBH) for planning CT and DIBH gated treatment delivery. PTV created by leaving margin around maximum tumor excursion observed under fluoroscopy. All of the answers provided are correct. Binning the CT into segments of the breathing cycle, and planning with selected segments.
PTC created by leaving margin around maximum tumor excision observed under fluoroscopy
The Beam Quality for a photon beam is defined in TG51 for use for determining KQ as: Tissue Air Ratio at 10 cm depth for a 10 x 10 cm beam Depth of Dmax for the beam Percent depth dose at 10 cm depth for a 10 x 10 cm beam Tissue Maximum Ratio at 10 cm depth for a 10 x 10 cm beam
Percent depth dose at 10 cm for a 10 x 10 cm beam
For questions below, match the type of therapy unit with the principle or feature associated with it (each of the options can be used only once), Proton Therapy Tomotherapy Cyberknife Linac-Based SRS
Proton Therapy-- Bragg Peak Tomotherapy-- MV CT Cyberknife-- Robotic Arm Linac-Based SRS-- Rotation with
Which of the following statements is true regarding proton therapy? The ratio of dose at depth of tumor to entrance dose increases with increasing tumor size. Protons have a finite range that is proportional to their energy. There is no neutron contamination in a proton beam. The lateral beam penumbra (perpendicular to the beam direction) is always narrower for a passively scattered proton beam than for a megavoltage photon beam.
Protons have a finite range that is proportional to their energy
Potential advantages of IMRT over 3-D conformal treatment include all of the following, except: Dose conformity for irregularly shaped volumes. Ability to treat a volume with a concave surface, conformally. Significantly lower hot spots in the PTV. Reduced OAR morbidity at conventional tumor doses. The possibility of dose escalation.
Significantly lower hot spots in the PTV
The Air Kerma Strength Sk, was a term introduced by the AAPM Report 51 to describe the following parameter Dose rate from a brachytherapy source Compare different isotopes to each other Source strength for a brachytherapy source Exposure rate from a brachytherapy source
Source Strength for a brachy source
For the following radiation detectors match the following applications with the appropriate radiation detector: (Choose the best match so that each detector and its application is best represented) TLD/OSLD Therapy verification film Diode Farmer Ion Chamber Options: Dose Monitor, Measure 2d..., beam scanning, calibration
TLD/OSLD -- Dose monitor Therapy verification film- measure 2d... Diode--- beam scanning Farmer Ion Chamber- calibrate
To ensure adequate coverage of the treatment volume with an electron beam, it is important to remember that: All isodose curves decrease in width with depth. The 90% isodose increases and the 20% isodose decreases in width with depth. All isodose curves increase in width with depth. The 90% isodose decreases and the 20% isodose increases in width with depth.
The 90% isodose decreases and the 20% isodose increases in width with depth
The Temperature-Pressure correction applied to the Ion chamber reading uses 22 degrees Celcius and 760 mm Hg as a reference because: The linacs are tuned to work best at that temperature and pressure The calibration factor for the calibrated ion chamber was determined at the above temperature and pressure, and therefore the reading needs to be corrected for different temperature and pressure conditions. The Linac or Co-60 teletherapy unit output is dependent on the temperature and pressure None of the answers are correct The electrometer used to measure the output has a temperature and pressure dependence
The calibration factor for the calibrate ion chamber was determine at the above temperature and pressure, and therefore the reading needs to be corrected for different temperature and pressure conditions
Exposure is: (Choose the statement below that most closely describes the definition) Only defined for charged particles below 3 MeV The charge liberated by photons in a given mass of air The absorbed dose multiplied by the quality factor The amount of energy in joules/kg transferred from a photon beam to a medium
The charge liberated by photons in a given mass of air.
The Anisotropy Factor/Constant in a brachytherapy dose calculation algorithm accounts for the following phenomenon: Inverse square fall-off of the number of γ rays Attenuation of γ rays in tissue Scatter of γ rays in tissue The differential attenuation of γ rays from the encapsulation around the source None of the other answers are correct
The differential attenuation γ rays from the encapsulation around the source
For patient-specific IMRT QA, measured dose distributions obtained with film or detector arrays can be compared with calculated dose distributions in terms of % dose difference and distance-to-agreement (DTA). Which of the following statements is false? The distance to agreement criteria compensates for dose differences in low-gradient regions. The dose difference tolerance is typically set at 3%. Complex intensity patterns with large dose gradients generally have lower scores. The score of the percentage of points that are within tolerance is typically 90 to 95%. The distance to agreement tolerance is typically set at 3 mm.
The distance to agreement criteria compensates for dose differences in low-gradient regions.
When calibrating a cobalt-60 therapy unit, the temperature and pressure are recorded. This is because: The temperature and pressure affect the output of the 60Co source The calibration equipment can only be used within a range of 5 C and 10 mm mercury, depending on the manufacturer The mass of air in the ionization chamber will be greater at high temperature and high pressure The mass of air in the ionization chamber will be greater at low temperature and high pressure The mass of air in the ionization chamber will be greater at low temperature and low pressure
The mass of air in the ionization chamber will be greater at low temperature and high pressure
For TG51 protocol, which of the following statement is NOT correct? The photon beam output is calibrated to be 1cGy/MU regardless of the field size or beam energy. Each beam energy requires an independent calibration It is required to perform TG51 calibration at least once a year The only acceptable medium for measurement is water
The photon beam output is calibrated to be 1cGy/MU regardless of the field size or beam energy
What happens if the bias voltage on an ionization chamber is too low? The reading is too low The reading is too high The reading will be correct if proper temperature pressure corrections are applied The reading will be zero
The reading is too low
The process of "calibrating" a linear accelerator radiation beam output involves measuring accurately the dose delivered in cGy/MU for the beam under calibration conditions, and: Tweaking the Linac Monitor Chamber gain such that the dose delivered under the normalization conditions is 1 cGy/MU Tweaking the Linac injection current (dose rate) such that the dose delivered under the normalization conditions is 1 cGy/MU None of the answers provided are correct Entering the dose per MU under normalization conditions into the treatment planning system Calling the Linac engineer to fix the linac if the dose delivered under the normalization conditions is not 1 cGy/MU
Tweaking the Linac Monitor Chamber gain such that the dose delivered under the normalization conditions is 1 cGy/MU
All of the following techniques will increase the neutron contamination in a proton therapy machine, except: Moving the range shifter or energy modulator closer to the patient. Increasing the primary proton energy. Placing the field-shaping collimator closer to the patient. Using a scanning beam instead of a scattered beam.
Using a scanning beam instead of a scattered beam.
All of the following are factors which make water an excellent phantom for muscle tissue, except: Density (grams/cc) Effective atomic number (Z) Physical density (g/cm3) Electron density Viscosity
Viscosity
When crystals of lithium fluoride TLD are exposed to radiation and then heated, they emit: Visible Light X-Rays Microwaves Electrons None of the other choices are correct
Visible Light
Intensity-modulated radiation therapy (IMRT) can be delivered using either "Step-and-Shoot" (segmental IMRT) or "Sliding Window" (dynamic IMRT) techniques. The major difference between these two methods is: "Step-and-Shoot" does not require a multileaf collimator (MLC). "Sliding Window" requires fewer monitor units. With "Sliding Window" the beam is not interrupted or held during MLC movement. "Step-and-Shoot" produces more neutron contamination. Only "Step-and-Shoot" requires inverse treatment planning.
With Sliding Window the beam is not interrupted or held during MLC movement
The output of a linear accelerator's photon beam is calibrated to be 1.0 cGy/MU. This calibration point is always at: Depth dmax, 100 cm SAD, 10x10 cm field size. A depth, distance, and field size specified by the physicist, consistent with data used for treatment planning. Depth dmax, 100 cm SSD, 10x10 cm field size. Depth 10 cm, 100 cm SSD, 10 x10 cm field size. Depth 10 cm, 100 cm SAD, 10x10 cm field size
a depth, distance, and field size specified by the physicist, consistent with data used for treatment planning.
Which of the following statement is true regarding %dd(10)x for photon beams? %dd(10)x is an important factor to determine beam quality %dd(10)x is measured with a 1mm lead filter under the gantry for 10MV photon beams All of the answers provided are correct %dd(10)x is equal to %dd(10) for 6MV photon beam %dd(10)x is greater than %dd(10) for 10MV photon beam, due to electron contamination
all answers provided are correct
A diode detector can be used for all of the following except: annual calibration of the output of a linac daily output checks of linacs as part of a QA program as a probe in scanning water phantom dosimetry system, where spatial resolution is important measurements of in vivo doses during treatment with an appropriate build-up cap
annual calibration of the output of a linac
Positron emission occurs in radionuclides which have an excess of: a Neutrons b Electrons c Positrons d Protons e Mesons
d. protons
The equipment required to calibrate a photon beam annual include all of the following except: Water Phantom Diode detector Calibrated Electrometer Calibrated Farmer Chamber
diode detector
The advantages of radiochromic film, as compared to radiographic film, for purposes of x-ray and electron dosimetry include all of the following, except: It requires a lower dose Its response (optical density vs. absorbed dose) is more linear It is nearly tissue equivalent It is relatively insensitive to visible light It does not require post irradiation processing
it requires a lower dose
Respiratory gating allows a linac to _____ . display an overlay of the simulation CT and cone-beam CT images acquire a real-time image during treatment use the lowest dose rate available limit beam-onto specific phases of the breathing cycle
limit beam-on to specific phases of breathing cycle
Proton beams have which of the following clinical advantages? Adjustable RBE No exit dose Less sensitive to positioning errors Easily generated from radioactive materials
no exit dose
Shown below are the general equations for different radioactive decay methods or nuclear interactions. Match the appropriate disintegration/interaction type from one of the following: Alpha Decay, (n,alpha) interaction, beta minus decay, Electron Capture, Positron Emission
pics didn't work look it up
Absorbed Dose is: The charge liberated by photons in a given mass of air The absorbed dose multiplied by the quality factor The amount of energy in joules/kg transferred from a photon beam to a medium Only defined for charged particles below 3 MeV
the amount of energy in joules/kg transferred from photon beam to a medium
Which of the following statements regarding the "f- factor" used in the traditional dose calculation model for brachytherapy sources is not true : The f-factor exhibits energy dependence The f-factor is the same for all brachytherapy sources The f-factor is not used in the TG-43 (new) dose calculation formalism The f-factor has units of cGy/R The f-factor is used to convert exposure rate to dose rate
the f-factor is the same for all brachytherapy sources
Electron equilibrium is said to exist in a small mass when: the number of x-rays entering the mass is equal to the number of x-rays leaving it absorption of radiation becomes exponential the build-up of dose begins to slow down the number of electrons entering the mass is equal to the number of electrons leaving it
the number of electrons entering the mass is equal to the number of electrons leaving it
An unsealed ion chamber is exposed under identical condition to the same amount of radiation in cities A and B. It has a lower charge reading in city A than in city B because: background radiation could be higher in city B the pressure might be lower in city A the temperature might be higher in city B the relative humidity might be higher in city B
the pressure might be lower in city A
What happens if the bias voltage on an ionization chamber is too low? The reading will be zero The reading is too high The reading will be correct if proper temperature pressure corrections are applied The reading is too low
the reading is too low
The following information is provided for Questions 2 through 5: A 9 MeV therapy electron beam has the following characteristics: Energy (MeV) 9 R50 (cm) 4.00 Rp (cm) 4.91 Dmax (cm) 2.36 Calculate the average energy of the beam at the following locations (please do not use rule of thumb for determining the answers): Beam energy at depth of 4.91 cm is ____________ MeV.
0.000000
500 mCi of a point source of Cs-137 is placed in an open container. The following are the pertinent information for Cs-137: Half Life = 30 years Exposure Rate Constant( Γ ) = 0.328 R-m2/Ci-h f factor = 0.963 cGy/R Calculate the dose rate to a person standing 500 cm from the source in cGy/hr
0.0063
Two x-ray films, each with optical density of 1.0, are placed on top of one another. The fraction of incident light transmitted through the "sandwich" is: 0.2 0.02 0.01 0.001
0.01
For above, what would the total dose to the person be, if they stood at the above location for 4 hours? Your answer needs to be in units of cGy.
0.0252
An Isotope undergoes radioactive decay for the duration of 2.5 half lives. The fraction of the original activity remains after decay is _______. (your answer should be entered to 4 places of decimal)
0.1768
As a rule of thumb, ______ mm of lead is(are) required per MeV to make an electron beam cutout of adequate thickness to stop the electron beam. 0.2 1 0.1 2 0.5
0.5
A PTW N30001 0.6cc Farmer ion chamber has a: N_{D,w}^{60Co} value of = 5.350 x 107 Gy/C. The electrometer correction factor is Pelec = 1.003. The calibration conditions are SSD=100cm, depth=10cm, field size = 10x10 cm2 The normalization conditions are SSD=100cm, depth at dmax=1.5cm, field size = 10x10 cm2 The water temperature is T=24 °C and the atmospheric pressure is p=745 mmHg. The ion recombination correction factor is Pion=1.002, The polarity correction factor is Ppol=1.000 First we calibrate the 6MV beam, at the calibration condition, we have %dd(10)x = %dd(10)=67.7% and the average electrometer reading is Mraw = 12.45 nC for 100 MU delivered. Please calculate the following questions, give answers with an accuracy of at least three significant digits.What is the dose per MU at the calibration condition (units cGy/MU)?
0.681
For the following questions, use the information provided below: A PTW N30001 0.6cc Farmer ion chamber has a N_{D,w}^{60Co}/D,w value of = 5.350 x 107 Gy/C. The electrometer correction factor is Pelec = 1.003. The calibration conditions are SSD=100cm, depth=10cm, field size = 10x10 cm2 The normalization conditions are SSD=100cm, depth at dmax=1.5cm, field size = 10x10 cm2 The water temperature is T=24 °C and the atmospheric pressure is p=745 mmHg. The ion recombination correction factor is Pion=1.002, The polarity correction factor is Ppol=1.000 First we calibrate the 6MV beam, at the calibration condition, we have %dd(10)x = %dd(10)=67.7% and the average electrometer reading is Mraw = 12.45 nC for 100 MU delivered. Please calculate the following questions, give answers with an accuracy of at least three significant digits. What is the value of kQ for this beam and this chamber? (answer in 4 significant digits)
0.9893
Many centers now use MR for treatment planning of intracranial SRS instead of CT. The advantages of MR include: 1. Better contrast of tumor and soft tissue within the brain. 2. More accurate tissue inhomogeneity corrections using MR than CT. 3. The ability to have different scan sequences with MRI to allow better visualization of tumor and edema. 4. Less spatial distortion for MR images compared with CT.
1 and 3 are correct
For a photon treatment at 100cm SSD, the ODI used for setup is in error by 0.5 cm. The dose at dmax is in error by 2% 0.5% 0.25% 1.0%
1.0%
A PTW N30001 0.6cc Farmer ion chamber has a: N_{D,w}^{60Co} value of = 5.350 x 107 Gy/C. The electrometer correction factor is Pelec = 1.003. The calibration conditions are SSD=100cm, depth=10cm, field size = 10x10 cm2 The normalization conditions are SSD=100cm, depth at dmax=1.5cm, field size = 10x10 cm2 The water temperature is T=24 °C and the atmospheric pressure is p=745 mmHg. The ion recombination correction factor is Pion=1.002, The polarity correction factor is Ppol=1.000 First we calibrate the 6MV beam, at the calibration condition, we have %dd(10)x = %dd(10)=67.7% and the average electrometer reading is Mraw = 12.45 nC for 100 MU delivered. Please calculate the following questions, give answers with an accuracy of at least three significant digits.What is the dose per MU at the normalization condition (units cGy/MU)?
1.0045
If the original activity of the Isotope in Question 13 above was 1.5 Ci, how much of this original activity has been lost to the radioactive decay in the above duration? (Answer required in mCi, please type your answer with 3 places of decimal)
1230.0 or 1250.0
An ionization chamber is used to measure the exposure in a photon beam. The measured exposure is 15 R. What is the absorbed dose to air at that point? 13.1 cGy 38.7 cGy 12.5 cGy 2.5 cGy
13.1 cgy
A dose of 180cGy is to be delivered to the 85% isodose depth on the central axis with the 9 MeV beam from the Linac. The applicator is 6 × 6 cm2, the SSD=100 cm, and the cutout factor is 1.05. Calculate the required number of MU. (Assume that the output factor for the 6 × 6 cm2 applicator is 1.0)
202.0
An Ir-192 HDR source that is being shipped back has an activity of 6 Ci. How many GBq of Iridium-192 should the physicist report on the shipping package? Your answer should be GBq.
222.0 GBq
Two Cs-137 sources, each 2.0 cm in length, are placed end to end. The activity of the sources are 15 mgRaEq each. Using the along-away table, determine the dose rate at the point A shown in the sketch below. Assume 1mm wall thickness and 1.4 cm active length Radium souces. The dose rate at point A from the source on the right is _______________cGy/h
26.655
If you are warming up a machine and ran daily output measurements, you would need to notify a physicist if your daily QA output is off by____ 10% 3% 0.5% 1%
3%
The following information is provided for Questions 2 through 5: A 9 MeV therapy electron beam has the following characteristics: Energy (MeV) 9 R50 (cm) 4.00 Rp (cm) 4.91 Dmax (cm) 2.36 Calculate the average energy of the beam at the following locations (please do not use rule of thumb for determining the answers): Beam energy at depth of 3 cm is ____________ MeV. (please provide answer in 2 decimal places)
3.5
Therapy proton beams have an energy range of _____ . 30- 250 keV 30- 250 GeV 3- 25 GeV 30-250 MeV 3-25 MeV
30-250 MeV
If the exposure at 50 cm from an x-ray target is 10 mR, the exposure at 75 cm is___mR. 6.7 22.5 4.4 15 0.7
4.4
The following information is provided for Questions 2 through 5: A 9 MeV therapy electron beam has the following characteristics: Energy (MeV) 9 R50 (cm) 4.00 Rp (cm) 4.91 Dmax (cm) 2.36 Calculate the average energy of the beam at the following locations (please do not use rule of thumb for determining the answers): Beam energy at depth of Dmax is ____________ MeV. (please provide answer in 2 decimal places)
4.67
Two Cs-137 sources, each 2.0 cm in length, are placed end to end. The activity of the sources are 15 mgRaEq each. Using the along-away table, determine the dose rate at the point A shown in the sketch below. Assume 1mm wall thickness and 1.4 cm active length Radium souces. The dose rate at point A from the source on the left is _______________cGy/hr
44.94
A 10 Ci 192Ir source from a high dose rate afterloader has a exposure rate of 3 R/hr at 1 m. It is placed at the center of a container of radius 30 cm. _______ - TVLs (tenth value layers) of shielding are required to reduce the exposure rate at the outer surface of the container to less than 2 mR/hr. (NOTE: 1 TVL shielding reduces the exposure rate by 1/10 th of unshielded exposure rate). 5 1 7 9 3
5
An exposure rate of 50 mR/hr is measured at a distance of 1 m from a source of radiation. The exposure rate will be 2 mR/hr at _______m. 20 5 25 15 2
5
The exposure rate constant for 137Cs is 3.3 R.cm2/mCi .h. The exposure rate at 3 m from a patient with a temporary insertion of 163 mCi (ignoring tissue attenuation) is: 36 mR/hr 0.36 R/hr 60 R/h 6 mR/h
6 mR/h
Using common rules of thumb, a 12 MeV electron beam has a range of ____ cm, and a 80% depth dose at approximately ____ cm. 4, 3 12, 4 6, 4 9, 6 12, 6
6, 4
A patient is treated with respiratory gating with a duty cycle of 25%. The treatment machine is running at 400 MU/min. Approximately how long does it take to deliver a 100 MU field? 120 seconds 40 seconds 20 seconds 80 seconds 60 seconds
60 seconds
For a 10x10 cm electron cone, using an energy of 12 MeV, the electron field size can be blocked down to _____ without significantly affecting the central axis depth dose. 9 x 9 cm 6 x 6 cm 8 x 8 cm 3 x 3 cm
6x6 cm
The total dose rate at point A from both sources is _______________cGy/hr
71.595
A radioactive source of strength 25.0 mCi and half-life of 74 days will decay to _____ mCi after 111 days. A:7.55 B: 8.839 C: 10.354 D: 70.71 E: 12.5
8.839
The following information is provided for Questions 2 through 5: A 9 MeV therapy electron beam has the following characteristics: Energy (MeV) 9 R50 (cm) 4.00 Rp (cm) 4.91 Dmax (cm) 2.36 Calculate the average energy of the beam at the following locations (please do not use rule of thumb for determining the answers): Beam energy at skin surface is ____________ MeV.
9
An electron of ____ MeV would be most suitable for treating a PTV extending to 3 cm below the surface, if the physician wants to treat to the 80% isodose level. 6 - 8 13 - 16 17 - 21 9 - 12
9-12
In an intensity-modulated radiation therapy (IMRT) plan, the physician requests that D95 of the planning target volume (PTV) be 95% of the prescribed dose. This means that: 95% of the PTV volume should receive at least 95% of the prescribed dose 95 cc of the PTV should receive at least 95% of the prescribed dose None of the other answers are correct The whole PTV should receive at least 95% of the prescribed dose.
95% of the PTV volume should receive at least 95% of the prescribed dose
The Radial Dose Function (T(r)) in a brachytherapy dose calculation algorithm accounts for the following phenomenon: A. Attenuation of γ rays in tissue from a brachytherapy source B. Scatter of γ rays in tissue from a brachytherapy source C. Inverse square fall-off of the number of γ rays from a brachytherapy source
A & B
Possible Units of "Exposure Rate Constant ( Γ )" are: (more that one choice A through D below are possible) A: R m2/Ci hr B: cGy/hr C: R cm2/mCi hr D: µGy m2 /hr
A and C
IMRT using MLC usually requires an increased number of monitor units compared with conventional radiation therapy because: Field margins are usually smaller. Of increased leakage through the MLC compared with cut blocks. IMRT is usually delivered with lower energy photons. A fraction of the treatment field is blocked at any given time.
A fraction of the treatment field is blocked at any given time
If the half-life of a radionuclide is 74 days, the decay constant is___________ A: 0.0094 per day B: 106.8 days C: 37 days D: 3.7 days E: 0.027 per day
A: 0.0094
Two nuclides have the following properties: Nuclide I Nuclide II Atomic number Z Z+1 Mass number A A Nuclide I may transform into Nuclide II by: A:Beta minus decay B: Isomeric transition C:Beta plus decay D: Alpha decay
A: Beta minus Decay
Cone-based arc stereotactic radiosurgery (SRS) systems offer all of the following advantages over static MLC-based SRS systems, except: Ability to easily treat asymmetrically shaped volumes conformally. Reduced transmission outside treatment field. Sharper penumbra. Less maintenance and QA compared with MLC.
Ability to easily treat asymmetrically shaped volumes conformally
X-ray contamination in electron beams is: Zero beyond depth Rp About 2% to 5% for a 16 MeV beam Mostly due to electron interactions in tissue. Highest for low-energy electrons
About 2% to 5% for a 16 MeV beam
131 Iodine and 125 Iodine: A. Occupy different columns on the periodic table B. None of the other answers are correct C. Have the same number of neutrons. D. Have different chemical properties E. Have different Z values
B. None of the other answers are correct.
Which of the following statements is not true regarding the Dose Rate Constant (Λ ) : A: Is defined as the dose rate to water at a distance of 1 cm on the transverse axis of a unit air kerma strength source in a water phantom B. Is the same for all brachytherapy sources that have the same encapsulation C. Is determined for every new source model that is introduced into the market D. Is specific to a source model E. Is expressed in units of cGy hr-1 U-1
B: is the same for all brachytherapy sources that have the dame encapsulation
Which of the statements below are correct for the following: X-Ray background in a therapeutic electron beam: Is produced primarily in the scattering foils in the treatment head Increases in magnitude (as observed in the tail of the PDD distribution) with increasing electron beam energy
Both are correct
Methods for producing large proton treatment fields include: Pencil beam scanning only Double scattering only None of the choices are correct Both pencil beam scanning and double scattering
Both pencil beam scanning and double scattering
The dose measured beyond the practical range of a therapy electron beam is due to: The highest energy electrons in the spectrum Very low-energy electrons Bremsstrahlung Characteristic x-rays generated in tissue
Brems
After 10 half-lives, the fraction of activity remaining is _________ A. 1-(1/2)10 B. 1 -e-0 .693 x 10 C. (1/2)10 D. e-0.693*10
C
A batch of I-125 seeds for a prostate implant is required to have an activity of 0.50 mCi/seed at the time of the implant. If the seeds arrive 5 days early, their activity will be _____ mCi/seed on arrival. (Half-life = 60 days.) A: 0.47 B: 0.59 C: 0.53 D: 0.77 E: 0.62
C: 0.53
During nuclear decay, energetic particles are emitted. The maximum energy of these particles is a function of the: A: Decay Constant B: Neutron capture cross section C:Mass Defect D: Spoin orientation of the particles.
C: Mass Defect
Geiger counters: Can detect very low levels of radiation down to individual photons or particles Can be used in high-intensity radiation fields Operate on the principle of scintillation Are less sensitive than ionization chambers
Can detect very low levels of radiation down to individual photons or particles
The quantity that an ionization chamber actually measures is: (Not what is ultimately derived from the measured quantity) Roentgen Kerma Voltage Charge Gray
Charge
The half-life of a radionuclide is: A Usually shorter for beta-minus than beta-plus emitters B Influenced by temperature and pressure. C Directly proportional to the decay constant. D Inversely proportional to the decay constant.
D Inversely Proportional to the decay constant
Which kind of radioactive equilibrium can occur when a very long-lived radionuclide decays to a short-lived daughter? A.Temporary B. Thermal C.Non-stable D. Secular E. Transient
D. Secular
"Exposure Rate Constant ( Γ )" is: A: A constant for all radioactive source B: Dose Rate in cGy per hour for a given activity at unit distance C: Measure of the strength of a radioactive source D: Exposure Rate in Roentgens per hour for a unit activity at unit distance
D: Exposure Rate in Roentgens per hour for a unit activity at unit distance
In the expression A = A 0 e ^− λ t , λ is ______________ A:The mass attenuation coefficient B: The linear attenuation coefficient C: The fraction of atoms decaying in time t D:The fraction of atoms decaying per unit time E:The number of atoms decaying per unit time
D: The fraction of atoms decaying per unit time
All of the following are true except: Tritium 3H ______ hydrogen 1H. A: has more neutrons than B: is chemically identical to C: is an isotope of D: has more electrons than
D: has more electrons than
Which of the following does NOT require a bias voltage applied? Plane-parallel ion chamber Survey meter Farmer ion chamber Diodes Proportional counter
Diodes
A TLD measures absorbed dose using the principle of Temperature changes in a medium Electrons trapped when material is irradiated, and given off as light when heated Chemical changes in chemical in solution containing Fe2+ ions None of the other answers are correct. Measuring the ionization current produced in a dosimeter
Electrons trapped when material is irradiated, and given off as light when heated
The Average lifetime for an isotope is numerically: Equal to 1.44 x T½ None of the answers are correct Equal to its half life (T½) Equal to 0.693/T½
Equal to 1.44 x T½
Which of the following radiation detectors would you use to calibrate a linac photon beam: TLD chip Farmer ion chamber Diode dosimeter Therapy Verification Film
Farmer Ion Chamber
Leaf positioning accuracy is critical for IMRT because: Round leaf edges found on many MLC increase leaf transmission at field edges. IMRT apertures are irregular in shape. MU are greater for IMRT fields. Dose reproducibility is more important for IMRT Gaps or opening between leaves determine the accuracy of the dose delivered and most IMRT treatments involve many small field openings
Gaps or opening between leaves determine the accuracy of the dose delivered and most IMRT treatment involve many small field openings
Compared with 6 MeV electrons, 16 MeV electrons have a: Lower bremsstrahlung tail Sharper fall off between 80% and the 20% isodose levels. Narrower plateau region around dmax. Greater surface dose Narrower penumbra
Greater surface dose
"Dwell Time", "Dwell Position", and "Dwell weight" are terms used in reference to: Brachytherapy Planning for Line Sources Low Dose Rate Brachytherapy Planning Medium Dose Rate Brachytherapy Planning High Dose Rate Brachytherapy planning
HDR Planning
When treating the buccal mucosa with an electron beam, a lead shield is inserted into the oral cavity. The change in dose expected in the tissue next to the proximal and distal surfaces of the shield, relative to the unblocked treatment, are: Increased dose at the front, decreased dose at the back Increased dose at both surfaces Decreased dose at both surfaces Increased dose at the back, no change at the front
Increased dose at the front, decreased dose at the back
As electron energy increases, surface dose _______ and depth of dmax _______. Decreases, increases Decreases, decreases Increases, increases Increases, decreases
Increases, Increase
For clinical measurement of the dose to a patient's pacemaker, diodes have the following advantage over TLDs: Smaller size Instant reading Greater accuracy More tissue equivalent
Instant Reading
Ion-recombination can be a problem when using a: Diodes TLD Polymer gel dosimeters Ionization Chambers Calorimeter
Ionization Chambers
The output (Dose per MU) for a clinical electron beam: Is measured and tabulated for every applicator (cone) used in clinical treatments Is independent of SSD Needs to be measured for every cut-out created irrespective of size None of the other answers are correct
Is measured and tabulated for every applicator (cone) used in clinical treatments
