RAPHEX X

Question 1

A calibrated 137Cs beam has an exposure rate of 2000 R/hr at 100 cm from the source. Given that 137Cs has a specific activity of 88 Ci/g and an exposure rate constant of 3.43 R cm2 / (mCi hr),
ANSWER
what is the mass of 137Cs in the source? A. 0.33 g B. 0.66 g C. 33 g D. 66 g E. 330 g

Answer 1

D. 66 g
2000 [R/hr] / 3.43 [Rcm2/mCi-hr] = 583.09 [mCi/cm2] 583.09 [mCi/cm2]  (100 cm)2  1/88 [g/Ci]  1/1000 [Ci/mCi] = 66 g

Question 2

The 60Co decay rate is approximately _____% per _____. A. 1; day B. 1; month C. 1; year D. 10; day E. 10; month

Answer 2

1 % per month

t1/2 = 365 days * 5.3 years
I/Io = 0.99964 for a day
(1-0.99964)X100% is daily loss

Question 3

In a nuclear reaction, the total mass of the final particles is 0.0015 amu LESS than that of the initial particles. This reaction results in _____MeV of energy _____.

Answer 3

C. 1.40; released Energy equivalent of 1 amu = 931 MeV. Q = 931 MeV  0.0015 = 1. 40 MeV. The above reaction is exoergic; that is, 1.4 MeV of energy is released.

Question 4

The advantage(s) of a 270o bending magnet in a linear accelerator include(s) _____. A. smaller electron spot size on the x-ray target B. higher electron beam energy C. higher average x-ray energy D. less cost and complexity in building the linac E. All of the above are true.

Answer 4

A. smaller electron spot size on the x-ray target The electron beam exiting the accelerating cavity typically has an energy spread of 1% to 2%. The 270o bending magnet allows proper focusing of electrons of slightly different energies and, therefore, a smaller spot size on the target. There is also less loss of electron beam intensity with the 270o bending magnet, albeit at increased complexity and cost of building the linac. When using only a 90o bending magnet, lower-energy electrons would be bent slightly more than higher-energy electrons, thus resulting in a large spot size on the x-ray target. A larger spot size would, in turn, result in a slight degradation of beam penumbra sharpness, which is undesirable

Question 5

The ion chambers in the linac treatment head monitor all of the following beam parameters except _____. A. dose rate B. energy C. integrated dose D. field symmetry E. All of the above are monitored.

Answer 5

B. energy The x-ray beam or the electron beam is incident on the dose monitoring chambers. The monitoring system consists of several ion chambers or a single chamber with multiple plates. Although the chambers are usually transmission type, i.e., flat parallel plate chambers to cover the entire beam, cylindrical thimble chambers have also been used in some linacs. The function of the ion chamber is to monitor dose rate, integrated dose, and field symmetry

Question 6

Which of the following statements regarding MRI-guided treatment units is FALSE? A. The radiation source can be either a 60Co source or a linear accelerator. B. Patients with metal implants can be treated on an MRI-guided unit. C. There is a reduced ability to use couch kicks than what is available on a conventional linac.
D. All of the above are true. E. None of the above is true.

Answer 6

B. Patients with metal implants can be treated on an MRI-guided unit. The first combined MR treatment units used 60Co because exposing the beam of electrons to an external magnetic field is a difficult engineering problem. Even within the patient, the presence of the magnetic field affects the delivered dose distribution due to the interactions of the secondary electrons with the magnetic field. Metal implants may be subject to heating as well as magnetic forces, and many implants are not safe for use in any MR unit.

Question 7

Which of the following statements regarding kV and MV photon production is FALSE? A. MV photon fluence production is more forward directed. B. Most MV beams utilize transmission targets. C. kV and MV beams experience heel effect. D. kV and MV x-rays can be created by accelerating electrons through an electric potential and hitting a target.
E. kV sources utilize a rotating anode.

Answer 7

C. kV and MV beams experience heel effect. The heel effect occurs due to nonuniform self-attenuation within the angled anode used in kV beam generation. MV beams utilize a uniform target and do not experience the heel effect.

Question 8

Multi-leaf collimators are usually constructed from _____. A. tungsten B. lead C. steel D. beryllium E. chromium

Answer 8

A. tungsten According to AAPM TG-50, multi-leaf collimators (MLC) are usually made of a tungsten alloy because it is hard, machinable, inexpensive, and has one of the highest densities of any material.

Question 9

An electron beam is most likely to interact with the _____ of an atom. A. inner shell electrons B. outer shell electrons C. nucleus D. proton E. neutron

Answer 9

B. outer shell electrons When a charged particle interacts with an atom, the influence of the particle’s coulomb force field affects the atom as a whole. Most of the interactions are “soft” collisions with outer shell electrons, transferring only minute fractions of the incident particle’s kinetic energy. This process is often referred to as the “continuous slowing-down approximation.”

Question 10

For which curve would the first and second HVL be closest in value as the beams traverse a homogeneous material? A. A B. B C. C D. All have the same difference between the first and second HVL. E. There is not enough information to answer the question.

Answer 10

B
For a mono-energetic beam, the HVL is constant. The narrowest energy spectrum in the figure represents the situation where the first and second HVLs will be the closest

Question 11

Which curve would see the largest increase in HVL with a low-energy filter placed in the beam? A. A B. B C. C D. No spectra would be affected. E. There is not enough information to answer the question.

Answer 11

A. A
Energy spectrum A has the largest proportion of low-energy components that would be removed by a low-energy filter. The other curves would be much less affected. Removal of this energy range would harden the beam and increase the HVL.B. Directly ionizing particles have a charge and can, therefore, ionize the atoms of the material via Coulomb interaction

Question 12

Pair production is a process by which a photon interacts with _____: A. a tightly bound orbital electron B. an essentially free electron C. the nuclear Coulomb field D. the neutrons in the nucleus E. None of the above is true

Answer 12

C. the nuclear coulomb effect Pair production occurs when a photon with energy above a threshold of 1.022 MeV interacts with the Coulomb field around a nucleus. The photon disappears, and an electron-positron pair is produced.

Question 13

If the transmission values for radiochromic films exposed to 0 cGy and 275 cGy are 5000 and 500, respectively, what is the net optical density corresponding to 275 cGy? A. 0.55 B. 1.00 C. 1.26 D. 2.00 E. This cannot be determined from information given.

Answer 13

1.00 The dose received by the film can be related to the amount of light that can pass through the exposed film. This is known as the optical density. Given Io and It as the transmission values measured before and after an exposure, the optical density can be defined as: OD = log10 (Io/It). In this example, OD = log10 (5000/500) = 1.000.

Question 14

Placing a single in-vivo dosimeter at the prescription point for a TBI treatment can verify that _____. A. the patient is at, or close to, the intended SSD B. the physician has prescribed the correct dose C. dose homogeneity is as expected D. All of the above are true. E. None of the above is t

Answer 14

A. the patient is at, or close to, the intended SSD TBI treatments are often delivered at extended SSDs, up to 400 cm, and in-vivo dosimetry can indicate whether the patient was positioned at the correct distance from the source. In-vivo dosimetry can inform the staff that the treatment was not being delivered as prescribed, but it cannot verify that the prescribed dose is correct. A single dosimeter at the prescription point cannot give information about the dose homogeneity throughout the patient. In that case, dosimeters would need to be placed at a number of locations along the body.

Question 15

Which of the following commissioning dosimetry tests would be most useful in determining the threshold for the minimum number of monitor units allowed for an individual subfield within a step-and-shoot delivery? A. machine output calibration B. beam profile constancy C. MU linearity D. output vs. gantry angle E. MLC spee

Answer 15

. MU linearity MU linearity tests would determine the minimum deliverable monitor units at which the ratio of dose to monitor units is consistent.

Question 16

Which of the following is NOT an advantage of a dynamic wedge compared to a physical wedge? A. central axis depth dose curve has less dependence on wedge angle B. less treatment time C. less outside-the-field dose D. better target coverage for treatment of moving tumor E. less beam hardening

Answer 16

better target coverage for treatment of moving tumor

A physical wedge changes the beam energy fluence of the primary x-ray beam through the insertion of a metallic filter at the gantry head, resulting in beam hardening and, hence, a stronger depth dependence of the wedge factor. The number of MUs used to deliver a particular dose using a dynamic wedge field is less than that used for a physical wedge field due to less attenuation of the primary radiation. Physical wedges create more scattered radiation outside the field, which arises from the interaction of the beam with the material of the physical wedge. The “interplay effect” is the result of the interplay between the moving tumor and the motion of the radiation beam as defined by the dynamic wedges (or IMRT) and can result in dose discrepancy. Dynamic wedges should be considered with caution before utilization for treatment in cases of respiratory organ motion

Question 17

230 MU are delivered for treatment prescribed to a depth of 5 cm with a single 6 MV field at 100 cm SSD. Under these conditions, the PDD = 87.0%.

Calculate the PDD for a depth of 5 cm, 120 cm SSD, and the same field size on the surface. A. 84% B. 86% C. 88% D. 90% E. 92%

Answer 17

88% The Mayneord F-factor can be used for the calculation of the PDD at the new SSD: P(d, r, f2 ) / P (d, r, f1) = (f2 + dm)2 / (f1 + dm)2 (f1 + d)2 / (f2 + d)2 = (120 + 1.5)2 / (100 + 1.5)2 (100 + 5)2 / (120 + 5)2 = 1.011
Using the Mayneord F-factor, the PDD for 120 cm SSD = 87%  1.011 = 88%.

Question 18

230 MU are delivered for treatment prescribed to a depth of 5 cm with a single 6 MV field at 100 cm SSD. Under these conditions, the PDD = 87.0%.

Calculate the MU to deliver the same dose at a depth of 5 cm, for a SSD of 120 cm, and the same field size on the surface. Ignore changes in the collimator scatter factor. A. 230 B. 276 C. 326 D. 330 E. 333

Answer 18

C. 326 When the SSD increases, the dose rate at dmax decreases following 1/r2, and the PDD increases because of the effects of the inverse square law. The dose/MU at dmax changes by: (100 + 1.5)2 / (120 + 1.5)2 = 0.698. The PDD for 120 cm SSD changes by the Mayneord F-factor: (120 + 1.5)2 / (100 + 1.5)2 . (100 + 5)2 / (120 + 5)2 = 1.011. The new MU for 120 cm SSD = 230 MU / (0.698  1.011) = 326 MU.

Question 19

Orthogonal junctions are created between the lateral brain fields and a posterior spine field in a craniospinal irradiation. The _____ is used to calculate the collimator rotation angle of the cranial fields so that their caudal field border is parallel to the cephalad border of the spinal field. A. cranial field size B. upper spinal field size C. lower spinal field size D. spinal field couch rotation E. upper spinal collimator angle

Answer 19

upper spinal field size This can be accomplished by rotating the collimator of the cranial fields through θcoll, where θcoll = arc tan [(L1 / 2) / 100] and L1 is the field size of upper spinal field.

Question 20

Orthogonal junctions are created between the lateral brain fields and a posterior spine field in a craniospinal irradiation. The _____ is used to calculate the couch rotation angle of the cranial field for matching between the spinal field and the diverging border of the cranial field. A. cranial field size B. upper spinal field size C. lower spinal field size D. cranial collimator angle E. upper spinal collimator angle

Answer 20

A. cranial field size To match the diverging cranial fields with the diverging spinal field, the couch needs to be rotated through θcouch in addition to the rotation of the cranial fields through θcoll. θcouch = arc tan [(L2 / 2) / 100]; L2 is the field size of cranial fields.

Question 21

Horns in the photon beam profiles are more pronounced for _____ MV photons, _____ field sizes, at _____ depths. A. 15; small; shallow B. 15; large; deep C. D. E.
6; large; deep
6; large; shallow 6; small; shallow

Answer 21

D. 6; large; shallow Field flatness for photon beams across the central 80% of the full width at half maximum of the profile in a plane is given by F = [(M – m) / (M + m)]  100%, where M and m are the maximum and minimum dose values in the central 80% of the profile, respectively. Standard linac specifications generally require that F be within 3% at a 10 cm depth in water. Low-energy and large-field-size photon beams have lower effective energies in off-axis directions, and they have more scattered dose contribution to the center of the field as the depth increases. Compliance with the criteria of 3% beam flatness at 10 cm depth results in “over flattening,” or “horns,” at shallow depths. This effect is more significant for larger-field-size beams.

Question 22

For photon fields, the geometric penumbra decreases as the source-collimation distance _____ and as the source-surface distance _____. A. increases; increases B. increases; decreases C. decreases; increases D. decreases; decrease

Answer 22

B. increases; decreases The geometric penumbra is given as P = s(SSD + d – SCD) / SCD, where P is the penumbra, s is the source size, SSD is the source-surface distance, d is the depth in the patient/phantom, and SCD is the source-collimation distance. From the formula, it can be seen that the penumbra will decrease with a decrease in SSD and an increase in SCD

Question 23

What is the best method to reduce the possibility of a skin reaction for a prone breast treatment when the apex of the breast is making contact with a treatment table? A. Close the anterior jaw to block the breast apex. B. Increase the beam energy to reduce the skin dose. C. Apply a 5-mm bolus. D. Apply a beam spoiler. E. Place thick, dry gauze between the apex of the breast and the treatment table.

Answer 23

E. Place thick, dry gauze between the apex of the breast and the treatment table. The skin reaction would be caused by scatter coming from the couch to the breast apex. Adding gauze would physically separate the breast from the couch, reducing the scatter dose. Closing the anterior jaw would block some of the target, so is not acceptable. Bolus and spoilers would increase the breast surface dose in general. Changing the beam energy would reduce the breast surface dose medially and laterally, but would not prevent the problem of scatter from the couch being incident upon the breast apex

Question 24

The dose at the isocenter (100 cm SAD), at a depth of 10 cm, is 200 cGy from equally weighted parallel-opposed anterior-posterior beams. Assuming that the patient separation is 20 cm, what is the dose at a depth of 5 cm from the anterior surface given the following TMRs?
TMR (d = 1.5) = 1.000 TMR (d = 5) = 0.920 TMR (d = 10) = 0.780 TMR (d = 15) = 0.640 TMR (d = 20) = 0.520
ANSWER
A. 202 cGy B. 205 cGy C. 208 cGy D. 211 cGy E. 215 cGy

Answer 24

205 cGy
Knowing the dose at one point, you can calculate the dose at any other by using the inverse square law and the ratio of TMRs. Each beam delivers 100 cGy to a depth of 10 cm. From the AP, the source-point distance is 95 cm, and from the PA, the source-point distance is 105 cm. Therefore, Dant depth=5 = {Dd=10 from AP  (100 / 95)2  [TMR(d = 5) / TMR(d = 10)]}AP beam + {Dd=10 from PA  (100 / 105)2  [TMR(d = 15) / TMR(d = 10)]}PA beam = 205 cGy

Question 25

what FS is used for Sc?

Answer 25

collimator setting (jaw size), not MLC defined FS

TMR and Sp use MLC defined field size

Question 26

What are the optimal wedge angles needed to create a uniform dose distribution for a pair of photon fields separated by a gantry angle of 120°?

Answer 26

30° The angular separation between the fields, 120° in this case, is defined as the hinge angle. The most appropriate wedge angle that results in the most uniform radiation dose for a given hinge angle is given by: Wedge angle = 90° – Hinge angle/2 = 90° – 120° / 2 = 3

Question 27

The dose calculated and displayed by most treatment planning systems (TPS) in the x-ray buildup region is not reliable. Why? A. The electron contamination in the beam is calculated using a very simple model or not modeled at all.
B. Measurement of the dose, for the purpose of TPS commissioning, in a region without charged particle equilibrium requires the use of a special dosimeter, which is often not readily available.
ANSWER
C. The calculated results will vary with the CT voxel size and the dose calculation grid size. D. All of the above are true. E. None of the above is true.

Answer 27

D. All of the above are true. If one intends on delivering prescription dose to the surface of the patient, bolus should be used. If one needs to verify that the skin is getting an appropriate dose, an in-vivo dosimeter should be used. The treatment planning system dose calculation in the buildup region is not reliably accurate

Question 28

A 12 MeV electron beam travels through 3 cm soft tissue and then 3 cm bone with a coefficient of equivalent thickness (CET) of 1.5. The geometric range of this electron beam is _____ cm. A. 3 B. 3.5 C. 4 D. 4.5 E. 5

Answer 28

E. 5
The CET (coefficient of equivalent thickness) method can be used to correct the depth dose change beyond a large and uniform inhomogeneity. The attenuation by a given thickness z of the inhomogeneity is equivalent to the attenuation (z  CET) of water. The range of 12 MeV electrons is 6 cm in water. The geometric range of 12 MeV electron beam in this case is 3 cm (in soft tissue) + (3 / 1.5) cm (in bone) = 5 cm

Water attenuates at 2 MeV/cm. Bone does it at 2*1.5 MeV/cm. Calculate from there

Question 29

Estimate the 90% depth of a 1010 cm2 9 MeV electron beam accounting for the fact that it travels through 0.5 cm of bolus before entering the patient. A. 1.80 cm B. 2.30 cm C. 2.80 cm D. 4.00 cm E. 4.50 cm

Answer 29

B. 2.30 cm The 90% depth of an electron beam is approximately the energy divided by 3.2, so for a 9 MeV beam, 9 / 3.2 = 2.8 cm. If the beam traverses 0.5 cm of bolus, the depth in the patient will be 2.8 – 0.5 = 2.3 cm.

Question 30

The minimum amount of lead necessary to internally shield normal tissue distal of a 4 cm thick buccal mucosal lesion when a 12 MeV electron beam is used is _____. A. B. C. D.
2 mm 4 mm 6 mm 8 mm
E. 10 m

Answer 30

A. 2 mm The mean electron energy decreases linearly with depth, such that after 4 cm the average
energy of the remaining electron beam is given by: E = E0 (1–z/Rp) or E = 12 MeV (1 – 4 cm/ 6 cm) = 4 MeV. As a rule of thumb, the minimum amount of lead necessary is given in millimeters as E (MeV) / 2. After traveling through a 4 cm lesion, the average energy of the beam will be 4 MeV, which implies that a minimum of 2 mm of lead is necessary.

Question 31

Why are the phantom line pairs oriented at a 45-degree angle relative to the graticule? A. This is to maximize imager area tested. B. The phantom should not be imaged with this rotation. C. This is to avoid interference/aliasing artifacts due to the construction of the imager panel. D. Vendor analysis software requires a rotated image set. E. None of the above is true.

Answer 31

C. This is to avoid interference artifacts due to the construction of the imaging system. Imagers are constructed as grids with finite resolution and detector/pixel spacing. Interference artifacts (also called aliasing) may occur for certain line pair and magnification combinations if overlaid in the same orientation as the imager’s rows and columns

Question 32

This phantom can be used for all of the following imager tests EXCEPT _____. A. resolution B. contrast C. slice thickness D. noise E. scaling

Answer 32

C. slice thickness
This is a planar image phantom and not used to assess slice thickness, which is a property of volumetric (3D) imaging.

Question 33

According to AAPM TG-142, which of the following criteria do NOT have tighter tolerances for SRS/SBRT over IMRT? A. localizing lasers B. treatment couch position indicators C. light/radiation field coincidence D. coincidence of radiation and mechanical isocenter E. All of the tolerances above are tighter for SRS/SBRT over IMRT.

Answer 33

C. light/radiation field coincidence Light/radiation field coincidence tolerances, both symmetric and asymmetric, are the same for both SRS/SBRT and IMRT. These tolerances are 2 mm or 1% on a side (symmetric), 1 mm or 1% on a side (asymmetric)

Question 34

Treatment delivery accuracy will be MOST affected by uncertainty in the simulation laser positioning for _____. A. an SBRT plan with daily kV-CBCT for setup B. an IMRT plan with a pair of daily orthogonal kV planar images for setup C. an IMRT plan with a pair of weekly orthogonal MV planar images for setup D. a 3D plan with daily kV-CBCT for setup E. a 3D plan with a pair of daily orthogonal kV planar images for setup

Answer 34

an IMRT plan with a pair of weekly orthogonal MV planar images for setup Uncertainty in simulation laser positioning indicates that the skin marks made in the simulator may not accurately reflect the position of the planned isocenter. Therefore, any setup that relies primarily on skin marks, such as the use of weekly orthogonal setup imaging, will be most affected by this uncertainty, whereas image-guided techniques that rely on frequent planar or volumetric imaging will be affected les

Question 35

____ does NOT require a daily output check based on AAPM recommendations. A. GammaKnife® B. A regular medical linac C. CyberKnife® D. TomoTherapy® E. All of the above should receive a daily output ch

Answer 35

GammaKnife® 60Co sources decay at a well-known constant rate of about 1% per month. The output is checked at the source exchange and on a monthly basis, as per AAPM Task Group 42. The other options on the list are all forms of linear accelerators, and AAPM Task Groups 142 (regular medical linac), TG-148 (TomoTherapy), and TG-135 (robotic linacs) recommend daily output checks.

Question 36

HIPAA regulations require that video monitor displays at the linac control console showing images of patient treatments _____. A. be no larger than 20 inches B. not be recorded or saved C. be shielded from public view D. All of the above are true. E. None of the above—HIPPA regulations do not cover th

Answer 36

be shielded from public view Any images from the treatment room that might reveal a patient’s identity must be kept confidential and hidden from public view. If images are recorded or saved, they must be treated as personal health information and protected in the same way that other treatment records are.

Question 37

DICOM imaging “headers” or “metadata” _____. A. contain information about exam acquisition or reconstruction parameters B. are anonymized to protect sensitive health information C. are extraneous and are removed before digital storage D. are formatted by individual vendors to ensure compatibility with their own software E. None of the above is true.

Answer 37

A. contain information about exam acquisition or reconstruction parameters DICOM is a standard that is designed to allow medical image data to be transferred between devices made by different vendors.

Question 38

What is a typical activity for an 192Ir source when it is first exchanged into an HDR afterloader? A.
B. C. D.
0.1 Ci 0.5 Ci 1.0 Ci 5.0 Ci
E. 10.0 C

Answer 38

they said 5 Ci, I say it is 10…

Question 39

Compared to lead, the advantage of acrylic for 90Y shielding is that acrylic _____. A. has a lower density B. has a lower atomic mass C. has a lower bremsstrahlung production cross-section D. All of the above are true. E. None of the above is true.

Answer 39

has a lower bremsstrahlung production cross-section 90Y is a beta emitter. The emitted electrons have a maximum energy of 2.28 MeV. Since
bremsstrahlung production increases with increasing energy and increasing atomic number of the material, lead is much more likely to produce x-rays while interacting with the 90Y betas than acrylic would.

Question 40

Which will result in the greatest decrease in dose outside of a linear accelerator bunker, behind a concrete primary barrier? A. double the thickness of the barrier B. double the distance from the linear accelerator C. halve the beam-on time D. add a maze E. None of the above is true.

Answer 40

A. double the thickness of the barrier Primary barriers for C-arm accelerators are typically ~4 TVLs, resulting in 10–4 beam transmission. Doubling the thickness of the barrier would double the number of TVLs, leading to 10–8 transmission. Doubling the distance will quarter the dose following the inverse square law. Halving the beam-on time will halve the dose, although it is usually not feasible to decrease the beam-on time for the purposes of radiation protection. Mazes are not typically applied to primary barrier shielding; they are placed on secondary barriers.

Question 41

Which of the following correctly lists tissues in order of increasing brightness in a T2-weighted MRI image? A. fat, bone, gray matter, white matter, CSF B. CSF, gray matter, fat, white matter, bone C. gray matter, fat, white matter, CSF, bone D. bone, fat, white matter, gray matter, CSF E. CSF, gray matter, white matter, fat, bone

Answer 41

D. bone, fat, white matter, gray matter, CSF T2 relaxation is a measure of how long it takes for the exciting spinning protons to fall out of phase. In a T2 weighted image, the CSF appears as bright white and bone appears as black.

Question 42

Compared to deformable image registration, rigid registration _____. A. is more computationally demanding B. allows for a more straightforward evaluation of registration quality C. is less reliable for inter-modality image registration D. All of the above are true. E. None of the above is true.

Answer 42

B. allows for a more straightforward evaluation of registration quality Since a rigid registration includes only translations and rotations, evaluating the quality of the registration is relatively straightforward, and it often involves the use of tools like spyglasses or overlaying the images. Deformable image registration includes warping of one image to another, and it is difficult to evaluate whether the warping is done correctly. Rigid registration is less computationally demanding and is a better option for inter-modality, e.g. CT to MR, image registration.

Question 43

Which of the following is TRUE about the differences between MRI and CT for prostate radiotherapy planning? A. The prostate gland can be delineated more accurately on CT. B. Motion artifacts are more likely on CT. C. Internal anatomical changes, such as bladder filling or rectal changes, are more likely to be observed over the course of a simulation CT scan.
D. All of the above are true. E. None of the above is true.

Answer 43

E. None of the above is true. On MR is it easier to see the difference between the prostate gland and surrounding soft tissues, so generally a delineation of the gland on MR would be more accurate than that on CT. On modern CT-scanners, a simulation CT scan covering the pelvis can be acquired in less than a minute, too short to observe bladder filling or rectal changes, and minimal motion artifacts are expected. However, MRI scan time is usually significantly longer, especially if multiple sequences are to be acquired. Therefore, motion artifacts and observed changes in bladder, rectum, or bowel shape or size are more likely to occur over the course of multiple MRI sequence acquisitions than over a single simulation CT scan.

Question 44

When the CBCT acquisition mode is switched from full fan to half fan, _____ should happen. A. a decrease in kV B. a decrease in mAs C. a change in filter from full bow-tie to half bow-tie D. a change in gantry rotation from 360 degrees to 180 degrees E. All of the above are true.

Answer 44

C. a change in filter from full bow-tie to half bow-tie Full-fan CBCT geometry is used when a small field-of-view (FOV) is to be captured. Since the entire volume to be imaged is in the beam, 180 degrees is a sufficient range of angles to capture the image. A full bow-tie filter is used. For a half-fan CBCT geometry, which captures a larger FOV for a given gantry angle, only half of the volume of interest is in the beam, so 360 degrees is needed. A half bow-tie filter is used.

Question 45

The typical dose from a pelvis kV-CBCT is on the order of _____. A. 0.02 cGy B. 0.2 cGy C. 2 cGy D. 20 cGy E. 200 cGy

Answer 45

2cGy

Question 46

Which of the following statements about ultrasound imaging is TRUE? A. Ultrasound images display the ultrasound signal attenuation properties of tissues. B. Bone has a lower ultrasound attenuation coefficient than muscle. C. Ultrasound is an ionizing radiation as it has a high frequency. D. In medical imaging, the direction of ultrasound wave propagation is parallel to the particle displacement in tissues.
E. The speed of sound is independent of the material being traversed.

Answer 46

D. In medical imaging, the direction of ultrasound wave propagation is parallel to the particle displacement in tissues. Ultrasound is a mechanical wave that does not produce ionizing radiation. The particles in the medium are displaced in a sinusoidal fashion but don’t propagate with the wave energy. The ultrasound images show the ultrasound reflection properties of tissues. The speed of sound depends on the material being traversed, and bone has a higher attenuation coefficient than muscle.

Question 47

In digital radiography, the pixel size is related to the _____ resolution and the pixel bit depth is related to the _____ resolution. A. temporal; spatial B. spatial; temporal C. spatial; contrast D. contrast; spatial E. contrast; tempora

Answer 47

spatial; contrast Spatial resolution is related to the ability to distinguish between two discrete objects that are next to each other in space. In digital radiography the spatial resolution is affected by the pixel size and spacing. Contrast resolution is related to the ability to distinguish between two different levels of image intensity. A pixel with a bigger bit depth can hold more information and, therefore, will improve the contrast resolution. Temporal resolution is the ability to resolve fast-moving objects in time, and it depends on how quickly the pixel values can be read out, so that they can acquire and record the next image.

Question 48

The irradiated volume defined in ICRU 83 is the tissue volume that receives _____. A. at least a dose selected and specified by the radiation oncologist as being appropriate to achieve the purpose of treatment
ANSWER
B. a dose that is considered significant in relation to normal tissue tolerance C. a dose that is at least 20% of the prescribed dose D. a dose that is at least 10% of the prescribed dose E. a dose that is at least 5% of the prescribed do

Answer 48

a dose that is considered significant in relation to normal tissue tolerance The irradiated volume is larger than the treated volume and depends on the treatment technique used.

Question 49

The planning target volume (PTV) margin can be reduced by all of the following techniques except _____. A. 2D kV orthogonal imaging B. kV CBCT C. MV CBCT D. IMRT E. real-time tumor-tracking systems

Answer 49

IMRT The PTV includes both internal margin (IM) and patient setup margin (SM) to compensate for internal physiologic movements and variation in size and shape, as well as patient setup uncertainties. All IGRT techniques can be used for PTV margin reduction. The use of IMRT alone does not warrant a reduction of PTV margin. IMRT has more impact on the dose gradient, which can result in less dose to a nearby OAR

Question 50

_____ is an appropriate clinical application of motion monitoring using optical surface imaging systems. A. Extremity irradiation B. Frameless linac-based radiosurgery C. Deep inspiration breath hold for left breast irradiation D. All of the above are appropriate clinical applications. E. None of the above is appropriate for clinical applications

Answer 50

D. None of the above is appropriate for clinical applications. Optical surface monitoring is an appropriate method to monitor the motion for treatment sites that are superficial, such as extremity or breast, or sites that have a very rigid connection between the surface and internal anatomy, such as the face and head with an intracranial lesion

Question 51

Knowledge-based treatment planning _____. A. can effectively reduce treatment planning time to zero and, therefore, obviates the need for a dosimetrist
B. uses National Comprehensive Cancer Network (NCCN) guidelines to automatically select CTV and PTV margins
ANSWER
C. utilizes previously treated plans to generate a model which can predict treatment planning results and guide optimization
D. incorporates on-treatment imaging data to account for anatomical changes and automatically revises the plan
E. designs treatment plans that are robust to internal anatomic changes

Answer 51

utilizes previously treated plans to generate a model which can predict treatment planning outcomes and guide optimization Knowledge-based treatment planning requires a library of past plans in order to predict the dose volume histogram (DVH) for the current patient. Some implementations feed that DVH prediction into an optimization engine to attempt to create a deliverable plan that results in that DVH.

Question 52

The following VMAT plans were all generated using the same beam model on the same patient. Which plan is most likely to fail patient-specific VMAT QA?

Answer 52

Plan B
Using the MU/dose as a measure of fluence modulation, plan B can be assumed to have a higher amount of modulation and smaller delivery apertures compared to the other plans.

Question 53

According to the American College of Radiology Practice Parameters for IMRT, patient-specific IMRT QA measurements should be performed _____. A. before the plan is completed by the dosimetrist B. between when the dosimetrist completes the plan and the physician reviews the plan C. prior to the start of treatment D. within the first three treated fractions E. prior to the end of the treatment cours

Answer 53

answer says c but we learned d…

Question 54

what is this

Answer 54

secular equiblibrium
-half life of parent is very very long

Question 55

Of the following procedures, _____ is NOT routinely performed in a cone-based SRS program. A. treatment planning B. a Winston-Lutz test C. a daily output check D. a safety interlock check E. a cone output factor measuremen

Answer 55

a cone output factor measurement Cone output factor measurement is a complicated task performed at the commissioning of the SRS program.

Question 56

The conformity index is a measure of normal tissue irradiated to _____ dose, and the gradient index is a measure of _____. A. high; dose rate B. high; dose falloff C. high; low dose to normal tissue D. intermediate; dose falloff E. intermediate; low dose to normal tissue

Answer 56

high; dose falloff The conformity index is the ratio of volume receiving prescription dose to the PTV volume, which measures the normal tissue irradiated to high dose. The gradient index is the ratio of volume receiving 50% (or 60%) prescription dose to the PTV volume, which reflects the dose falloff.

Question 57

As compared to 125I for prostate seed implants, 103Pd has _____. A. greater spread of isodose lines, which produces better coverage B. the need for fewer seeds per implant C. shorter time required post-implant to observe radiation precautions D. All of the above are true. E. None of the above is tru

Answer 57

All of the above are true. A shorter half-life (17 days for 103Pd versus 59 days for 125I) means the sources will decay faster, and patients will need to observe precautions for a shorter window of time. 103Pd has the biological advantage of a higher initial dose rate and a shorter total treatment time

Question 58

Differences in the active source design for 125I seeds affect all of the following parameters EXCEPT _____. A. radial dose function B. air kerma rate constant C. decay constant D. anisotropy function E. All of the above depend on the design of the seed.

Answer 58

decay constant The decay constant depends only on the radioactive isotope, not the design of the source.

Question 59

Intravascular brachytherapy is often used _____. A. in emergent settings to open blocked coronary arteries B. in non-emergent settings to treat blocked arteries after drug-eluting stents have failed C. during open heart surgery to irradiate the surgical bed D. to treat supraventricular tachycardia E. None of the above is true

Answer 59

in non-emergent settings to treat blocked arteries after drug-eluting stents have failed

Question 60

Intravascular brachytherapy is often used _____. A. in emergent settings to open blocked coronary arteries B. in non-emergent settings to treat blocked arteries after drug-eluting stents have failed C. during open heart surgery to irradiate the surgical bed D. to treat supraventricular tachycardia E. None of the above is true

Answer 60

intraoperative electron radiotherapy with linear accelerators The goal of intraoperative radiotherapy (IORT) is to deliver a single high dose of radiation at the time of surgery to enhance tumor control. For HDR IORT, surface applicators are placed in patients and have guide tubes through which the HDR source travels. An example is the HAM applicator. There are two low-kV x-ray devices currently used for IORT, though these two systems share similarities in the way x-rays are produced. One device accelerates an electron beam to the end of a tube where it hits a gold target, with spherical or flat applicators attached to the source pole. The other low-kv x-ray system uses a miniature x-ray tube in a water-cooled catheter, and it is classified as electronic brachytherapy. Intraoperative electron radiotherapy (IOERT) uses electron beams produced from a mobile linac. MV photon energy is too high for IORT

Question 61

A vaginal cylinder treatment was planned to deliver 600 cGy to 0.5 cm into the vaginal tissue using a 2.6 cm diameter cylinder. However, a 3.0 cm diameter cylinder was used for treatment. What is the delivered dose to a point 0.5 cm into the vaginal tissue at a place in the center of the cylinder length? A. 486 cGy B. 540 cGy C. 600 cGy D. 667 cGy E. 741 cGy

Answer 61

540 cGy The vaginal cylinder can be approximated as a line source. The dose for a point of interest in the center of the length of that line source and a perpendicular distance r away, will fall off as 1/r. In the plan using a 2.6 cm diameter cylinder, the distance from the source to the prescription point would be 2.6 / 2 + 0.5 = 1.8 cm. However, for the delivery it was 3.0 / 2 + 0.5 = 2.0 cm. Therefore, the delivered dose would be 600  (1.8 / 2) = 540 cGy.

Question 62

_____ material should be used to lower proton beam energy with minimal impact on scatter. A. Low-Z B. High-Z C. Low magnetic permeability D. High magnetic permeability E. Material-independent

Answer 62

Low-Z
Low-Z materials will modify beam energy with minimal scattering, whereas high-Z materials will scatter the beam with less energy reduction.

Question 63

The proton range is defined _____ of the spread-out Bragg Peak. A. on the proximal side B. on the distal side C. at the center D. as the width E. None of the above is true.

Answer 63

on the distal size The range of a proton beam is defined on the distal side of the spread-out Bragg Peak (SOBP). The width of the SOBP is known as the mo

Question 64

Robustness in proton treatment planning refers to insensitivity of the PTV and organ-at-risk doses to changes in _____. A. range uncertainty B. patient setup uncertainty C. internal anatomy D. All of the above are true. E. None of the above is true

Answer 64

D. All of the above are true. Plans can be optimized to accommodate potential changes in range, patient setup, and internal anatomy (e.g., filling of nasal cavity, changes in respiration). The latter requires additional input data in the form of synthetic CTs or 4DCT. These plans may be less conformal than less robust plans, but provide plans that actually deliver the doses requir

Question 65

Interplay effects in scanned beam proton therapy can be mitigated by _____. A. breath hold B. respiratory gating C. layer and volumetric repainting D. All of the above are true. E. None of the above is true

Answer 65

D. All of the above are true. Interplay effects occur when scanning proton beams interact with moving patient anatomy, creating hot and cold spots. Breath hold and respiratory gating reduce internal patient motion. Repainting refers to delivering the proton beam multiple times, thereby averaging out the delivery.

Question 66

An unrecoverable error occurred after 75% of the last fraction of a 5-fraction 192Ir HDR brachytherapy procedure was delivered. It was determined that the target volume received only 65% of the prescribed dose for that fraction. As per the NRC, this can be considered _____. A. a non-event B. a recordable, not reportable event C. a reportable event D. a misadministration E. There is not enough information to answer the question

Answer 66

a recordable, not reportable event Because the delivered dose in one single fraction deviated by less than 50% of the intended dose AND the total dose to be administered deviated by less than 20% of the prescribed total dose, this qualifies as a recordable, not reportable, event

Question 67

In failure modes and effects analysis (FMEA), the risk priority number (RPN) is defined as the _____. A. frequency of occurrence of the failure B. severity of the failure C. detectability of the failure D. All of the above are true. E. None of the above is true.

Answer 67

None of the above is true. The RPN is the level of risk to the patient if the failure goes undetected. The RPN is the product of the calculated frequency of occurrence, severity, and detectability of the failure, and different failure modes can be ordered by their calculated RPNs.

Question 68

Which of the following is least appropriate for inclusion in the FMEA process map for daily IGRT? A. rectum/bladder filling different from sim B. image-guidance shifts off by 5 mm C. daily machine output deviation D. patient movement after imaging E. patient movement during delivery

Answer 68

daily machine output deviation Although daily machine output deviation may lead to dosimetric differences, it is outside the scope of an IGRT workflow and, therefore, would not be part of a daily IGRT process map.