additional questions for review – 2d & 3d · 2019-09-20 · additional questions for review...

Additional Questions for Review – 2D & 3D

1. For a 4-field box technique, which of the following will deliver the lowest dose to the femoral heads?

a. 100 SSD, equal dmax dose to all fields b. 100 SSD, equal target dose to all fields c. 100 SAD, equal air dose to all fields d. 100 SAD, equal target dose to all fields e. 100 SAD, equal monitor unit setting for all fields

2. Assuming the surgeon has left clips in the tumor bed following an

excision of a left breast tumor and an axillary dissection, the electron boost volume and depth may be accurately localized by:

I. obtaining a CT scan to show the location of the clips II. outlining the excision scar with lead wire and measuring the

chest wall distance on tangential simulator films III. taking orthogonal films and plotting the location of the clips on

the patient contour IV. measuring the depths from the clips to the skin and the chest wall

using tangential simulator films

a. 1, 2, and 3 b. 1 and 3 c. 2 and 4 d. 4 only e. All are correct

3. Conventional record and verify systems have made it possible to

perform daily computer confirmation of which of the following? I. patient position

II. treatment area III. isocenter location IV. collimator angle and field size


4. An optimized plan consists of three fields weighted 1.0 : 0.5 : 0.5 at the isocenter. The plan was normalized to the isocenter and the radiation oncologist prescribed 4500 cGy in 25 fractions to the 95% isodose line. What daily doses are required to produce a new dose distribution that shows the prescribed dose?

a. 90 : 45 : 45 b. 90 : 60 : 60 c. 95 : 47 : 47 d. 102 : 51 : 51 e. 120 : 30 : 30

5. When simulating tangential fields to treat a breast tumor, including

the internal mammary nodes, the medial field edge is set 3 cm to the contralateral side and the lateral field edge is set to encompass all of the breast tissue. If too much lung is traversed by these fields, a correction may be made by doing which of the following? I. moving the medial field edge toward the contralateral side

II. moving the lateral field edge posteriorly III. using a steeper collimator angle IV. using a separate internal mammary field with matching tangentials


6. Caution must be applied when using MRI for treatment planning

because: I. patient anatomy may appear distorted on the images

II. external contours are sometimes unreliable III. the brightness of the image is not related to tissue density IV. it is not reliable for locating tumors within tissue


7. Disregarding the effects of tissue inhomogeneity can result in errors in delivered dose that are:

I. inversely dependent on photon energy II. directly dependent on the dimensions of the inhomogeneity

III. dependent on the depth of the inhomogeneity IV. insignificant at 4 MV


8. Which of the following is/are appropriate treatment techniques for

delivering a boost dose of 26 Gy to a left anterior primary brain tumor following whole brain irradiation on a 6 MV linear accelerator? I. parallel opposed lateral fields, weighted 2:1 left to right

II. single 6 MeV left lateral electron field III. wedge pair, 45 degree wedges, 90 degree hinge angle IV. parallel opposed anterior and posterior fields


9. To make inhomogeneity corrections in treatment plans based on CT

derived anatomical information, the dosimetrist: a. converts CT numbers to Hounsfield units b. determines the absorption equivalents c. converts to equivalent path lengths d. determines electron densities e. determines mass attenuation coefficients

10. When simulating anteroposterior fields for whole abdominal treatment to 35 Gy, which of the following organs need to be localized so they can be shielded at their tolerance doses? I. kidneys

II. stomach III. liver IV. heart


11. In the small volume treatment of bladder cancer with radiation

therapy, the patient should be treated with: a. a full bladder in order to spare as much bowel as possible b. a full bladder in order to spread the dose evenly to the tumor c. an empty bladder in order to encompass tumor with

reproducibility d. an empty bladder in order to minimize bleeding complications e. the rectum empty

12. A 20 cm diameter patient is treated to mid-plane by using a 100cm

SAD technique. If the same patient is then treated by using a 100cm SSD technique, the monitor units would increase approximately:

a. 5% b. 10% c. 15% d. 21% e. 25%

13. The most significant effect(s) of an air cavity in a megavoltage beam treatment is/are: I. a change in the spectral energy distribution within the cavity

II. increased primary photon transmission through the cavity III. enhanced absorption of dose in and beyond the cavity IV. a partial loss of electronic equilibrium at the cavity interface


14. Compared with a standard static wedge, a dynamic wedge can:

I. produce a 10 degree wedge angle II. have shaper penumbral regions

III. be produced using MLCs IV. have significantly different transmission factors as a function of

field size a. 1, 2, and 3 b. 1 and 3 c. 2 and 4 d. 4 only e. All are correct

15. When treating a breast tumor, scattered dose to the opposite breast can

be reduced by: I. using a beam splitter in the tangential field

II. adding bolus to the treated breast III. reducing the amount of lung in the tangential fields IV. eliminating the wedge in the medial field


16. When simulating a plan utilizing Beam's Eye View treatment planning, it is necessary to: I. verify that the patient's position and alignment are equivalent to

those at the CT plan acquisition II. place the isocenter accurately in three dimensions with the aid of

the CT scout image and the data from the planning "slice" III. verify the isocenter with an orthogonal pair of radiographs for

future comparison to port films IV. use normal anatomy visible on radiographs and in particular bony

landmarks to verify correctness of the simulation


17. Which of the following statements is/are true concerning a 3-

dimensional (3D) pencil beam calculation algorithm? I. It does not consider the effects of scatter to and from

heterogeneities, irregular surfaces, or irregularly blocked fields II. It divides the broad beam into many small thin beams that can have

their own intensity and lateral scatter spread III. It uses an equivalent pathlength calculation that converts any

heterogeneity into homogeneous water medium through an attenuation equivalent thickness coefficient

IV. It allows each pencil beam to be individually manipulated to make the calculation more sensitive to changes in patient anatomy in all three dimensions


18. Dose Volume Histograms (DVH) are useful to: I. provide a graphic display of dose to the target

II. optimize the radiation treatment in a reasonable time III. give a good representation of the dose received by the normal

structure IV. indicate precisely the extreme dose (hot spot) in the volume treated


19. Clinical applications of MLC include which of the following?

I. shaping of static fields as a replacement for cerrobend blocks II. dynamic field shaping as a function of gantry rotation

III. modulating beam intensity by dynamic MLC IV. field shaping without penumbra


20. MLCs are advantageous over conventional field shaping devices

because: I. there is no danger of injury to the patient or therapist from a falling

block II. they eliminate toxicity concerns resulting from fabrication and

handling of lead and cadmium alloy blocks III. they save block fabrication costs, storage space, and the effort of

lifting and mounting heavy blocks IV. immediate modification of the field aperture can be made if the

portal image reveals inaccuracy


21. Radiographs that are generated from CT data in a plane perpendicular to the central axis of a simulated beam of radiation and used as reference images for verification of a computer-designed treatment are known as:

a. portal images b. digitally reconstructed radiographs (DRR) c. dose volume histograms d. multileaf collimation portals e. computed radiographs

22. Stereotactic Radiosurgery can be performed using:

I. photons II. protons

III. Cobalt-60 IV. electrons


23. Advantages of MLC compared to conventional cerrobend blocks

include: a. sharper penumbra b. lower leakage radiation c. can accommodate larger field sizes d. permits IMRT e. all of the above

24. The tongue-and-groove effect is related to which of the following:

a. an increase in dose between two adjacent leaves of a multileaf collimator

b. a most pronounced field-size effect on the output factor c. a decrease in the overall radiation fluence by about 1% d. it may be absent in some multifleaf design e. none of the above

25. According to the dose-volume histogram shown, all of the following are true except:

a. the minimum dose to this volume is approximately 30% b. 50% of the volume receives at least 75% of the dose c. 75% of the volume receives at least 50% of the dose d. 25% of the volume receives at least 75% of the dose e. part of the volume receives 100% of the dose

26. The fundamental difference between IMRT and 3D conformal

radiation therapy is: a. In IMRT, the intensity distribution of each beam is optimized

and is usually non-uniform. In 3DCRT, the intensity distribution is either uniform (as in open fields) or linear (as in wedged fields)

b. The number of beams used in a plan is usually more in IMRT than that in 3DCRT

c. The beam directions are non-coplanar for IMRT and coplanar for 3DCRT

d. The delineation of targets and critical organs are different between IMRT and 3DCRT

27. 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:

a. “step and shoot” does not require a multileaf collimator b. “sliding window” requires fewer monitor units c. only “step and shoot” requires inverse treatment planning d. only “sliding window” can deliver continuously variable dose

intensities e. “step and shoot” produces more neutron contamination

28. Inverse treatment planning usually does not incorporate:

a. specification of dose volume constraints b. Beam’s Eye View (BEV) computer display for design of field

sizes c. Intensity modulated beam delivery d. Monte Carlo dose calculations e. CT simulation

29. Match the imaging modality with its approximate spatial resolution in

the axial plane (choice may be used more than once): I. 0.5 – 1.0 mm

II. 1 – 2 mm III. 3 – 4 mm IV. 5 – 6 mm

a. CT I b. MRI I c. PET III

30. Advantages of EPID images compared to conventional portal films

include all of the following except: a. improved spatial resolution b. improved latitude c. improved contrast d. real-time image display e. digital image storage

31. For stereotactic radiosurgery, accuracy and reproducibility should generally be on the order of ____ mm.

a. 7 b. 5 c. 2 d. 0.5

32. The gamma knife could be incorporated into the treatment of all of the

following sites except: a. certain patients with two brain mets, each measuring 2.0 cm in

diameter b. a 1.5 cm intra-auricular acoustic neuroma c. a newly diagnosed GBM measuring 5 cm d. a 1.0 cm surgically inaccessible arteriovenous malformation

33. A lumpectomy site in the breast is treated with parallel opposed 6MV

photon fields, as shown below. On the DVH, 10% of the PTV receives less than 90% of the prescribed dose. The most probable reason for this is:

a. the field arrangement and choice of angles could be improved b. the fields are not wide enough to cover the PTV c. the beam energy is too low d. the PTV is drawn up to the skin, and includes the build-up

region

34. A radiotherapy department has a choice of 6, 10, and 18 MV photons. For IMRT prostate plans, _____ MV photons are chosen, because:

a. 6, this delivers the most homogeneous dose to the PTV b. 10, this delivers a lower neutron dose than 18 MV, but

acceptable dose to normal tissues c. 18, this delivers the lowest neutron dose and the lowest normal

tissue dose outside the PTV d. 10, although this delivers the highest neutron dose, it gives the

best dose distribution, and the neutron dose is clinically acceptable

35. Potential advantages of IMRT include all of the following except:

a. dose conformity for irregularly shaped volumes b. the possibility of dose escalation c. reduced normal tissue morbidity at conventional doses d. ability to treat a volume with a concave surface, conformally e. simpler verification of dose calculation and delivery

36. In IMRT inverse planning for treatment with the “step and shoot”

technique, all of the following are specified by the human planner (i.e. not by the computer), except:

a. beam angles b. number of beams c. beam weights d. dose constraints for contoured volumes e. PTV contour on CT images

37. Reasons for fusing an MRI scan with a CT scan for treatment

planning brain tumors include all of the following except: a. some brain lesions have areas of infiltration that are better

visualized on MRI b. CT is less subject to geometrical distortion than MRI c. image fusion should be more accurate than estimating contours

on CT using a hard copy of the MRI d. the CT image is required for heterogeneity corrections

38. All of the following are true regarding PET used in treatment planning except:

a. PET/CT can aid in treatment target definition b. PET images can show areas of metabolic activity c. 18F, a cyclotron produced positron emitter, is used in most PET

studies d. registration of PET and CT images can be a problem, which the

combined PET/CT unit is designed to solve e. an advantage of the combined PET/CT unit is that it makes

gating unnecessary

39. The execution of a conformal plan requires more attention to which of the following, compared to conventional planning? I. patient repositioning accuracy

II. MU calculations III. immobilization during treatment IV. choice of beam energy

a. 1, 2, and 3 b. 1 and 3 c. 2 and 4 d. 4 only e. all of the above

40. Non-coplanar arcs are traditionally used in linac radiosurgery because:

a. the calculation is easier b. geometric accuracy is more easily achieved with arcs c. the dose distribution can be made to conform to irregular

shapes d. they produce relatively rapid and symmetric dose fall off

outside the target e. treatment time is fast

41. Which of the cumulative DVH curves below represents the more homogeneous dose to the target volume, for a prescribed dose of 50 Gy?

a. curve A b. curve B c. cannot tell from the

information given

42. Approximately what percentage of the target volume below received a dose less than 60 Gy?

a. 0% b. 10% c. 20% d. 50% e. 80%

43. A dose volume histogram (in integral form) for PTV gives a. what percentage of PTV receives at least the prescribed organ

dose b. spatial distribution of dose in the organ c. amount of dose delivered outside the organ volume d. none of the above

44. A dose volume histogram

a. helps in optimizing the treatment plan b. is the only method of optimizing treatment plans c. is the best method for optimizing treatment plans d. is a totally objective tool for optimization

45. Stereotactic procedures: I. are generally used to treat brain lesions

II. involve the same immobilization devices as in the treatment of head and neck cases

III. involve accurate clinical target localization techniques IV. are used only for the treatment of malignancies

a. 1, 2, and 3 b. 1 and 3 c. 2 and 4 d. 4 only e. all are correct

46. In stereotactic treatment procedures:

I. the setup accuracy is much more important compared to conventional treatment procedures

II. the target volume can often be identified from conventional simulation and portal imaging procedures

III. noncoplanar beams are normally used IV. avoiding critical structures bordering on the target volume is not of

great importance


47. In treatment planning, when dose delivery parameters are computed

based on target-dose-delivery and normal tissue avoidance criteria, the process is termed ________ planning.

a. forward b. inverse c. reciprocal d. reverse

48. IMRT is a treatment planning and delivery process that seeks to achieve treatment plan optimization by varying the __________ of treatment beams in addition to their position.

a. field size b. intensity c. area d. energy

49. Image ______ is a process by which images produced by different

modalities can be combined to use the best features of each modality. a. production b. fusion c. registration d. none of the above

50. The quality of DRRs can be improved by ________ the thickness of

CT slices. a. increasing b. decreasing c. rotating d. multiplying

51. A plan-evaluation tool that simultaneously presents dose and volume

information in a graphical form allowing objective plan assessment is the dose volume histogram.

a. true b. false

52. Stereotactic radiotherapy is a treatment technique that involves:

I. delivering dose to small stereotactically localized targets with high precision and accuracy

II. target localization within about 1 mm III. accuracy of dose delivery within about 5% IV. dose delivery in the range of 1000 to 5000 cGy depending on

target size


53. The stereotactic radiotherapy technique I. treats functional disorders in brain

II. delivers dose as a single fraction III. treats small benign or malignant masses in the brain IV. involves patient simulation for precise localization of PTV; patient

must use stereotactic head frame for the precise localization and dose delivery


54. Stereotactic treatments are carried out with: (choose best answer)

I. a Gamma Knife II. a Co-60 unit

III. a linear accelerator with suitable accessories and modifications IV. a linear accelerator


55. For a 6 MV photon beam used for stereotactic radiosurgery, the

minimum beam size diameter (in mm) required for electronic equilibrium is about:

a. 5 mm b. 10 mm c. 15 mm d. 30 mm

56. For optimum irradiation of stereotactic lesions: I. POP fields must be made use of

II. as many beams as possible are used isotropically in the hemisphere surrounding the lesion

III. spherical dose distribution is necessary IV. Gamma Knife source configuration is an example


57. Use of cylindrical tertiary collimators in stereotactic radiotherapy:

I. provides more precise collimation II. gives rise to a spherical dose distribution surrounding the target

volume III. gives sharper dose fall-off compared to secondary collimators IV. is ideal for the treatment of all lesions


58. The linac-based stereotactic treatment procedures are:

I. single plane transverse rotation II. multiple noncoplanar converging arcs

III. single arc dynamic rotation IV. none of the above

a. 1, 2, and 3 b. 1 and 3 c. 2 only d. 4 only

59. Dose volume histograms for the target volumes and organs at risk should be reported for 3DCRT treatments.

a. true b. false

60. Electronic portal imaging can be used for the evaluation of setup

errors. a. true b. false

61. Digitally reconstructed radiographs (DRR) can be compared with

simulator films to verify the accuracy of beam placement. a. true b. false

62. DRRs can be compared with port films to ensure the accuracy of

treatment delivery a. true b. false

63. A beam’s eye view (BEV) helps the oncologist to see on the monitor

that the beam adequately covers the target volume. a. true b. false

64. The user can choose different calculation algorithms in the Treatment

Planning System depending on the accuracy required. a. true b. false

65. The desired dose uniformity in PTV as per ICRU-50 is

a. ± 1% b. ± 2% c. ± 3% d. ± 5%

66. In IMRT plans, wedges ______. a. can be used as compensators in wedged pairs of fields. b. are used to compensate for missing tissue in the sup/inf

direction. c. are generally not used d. of 60° are generally not used

67. A physicist is double-checking the MU for a computer-generated plan

of breast tangents, using a reference point in the center of the breast. The hand calculation gives a lower MU setting by 3%. A possible reason for this is:

a. lack of scatter to the reference point from the part of the tangent in air is accounted for in the plan, but not in the hand calculation.

b. the plan is calculated using a rectangular field, while the hand calculation uses an equivalent square field

c. beam hardening in tissue is not accounted for in the hand calculation

d. the hand calculation does not correct for increase scatter from the lung/chest wall interface

68. Advantages of treating intracranial lesions with linac-based

stereotactic radiosurgery versus conventional fractionated radiotherapy include all of the following except:

a. improved immobilization with the head frame b. reduced dose to normal brain tissue c. improved accuracy of localization d. smaller dose per fraction

69. Which of the following statements is false regarding linac-based

stereotactic radiosurgery? a. the diameter of the collimators varies from 5 mm to about 4 cm b. multiple arcs are typically used in treatment c. more than one isocenter may be used d. accuracy of tumor localization and geometric accuracy of dose

delivery should be of the order of 5 mm e. photon energies below 10 MV are typically used

70. Use of MLCs can save considerable fabrication and set-up time compared with cerrobend blocks. However, MLCs are not always ideal; all of the following are situations in which cut blocks would be required except when:

a. island blocks, such as larynx blocks are required b. the shape of the blocked areas requires a collimator angle which

conflicts with the direction of the dynamic wedge, on a unit for which only dynamic wedges are available

c. a 5 x 5 pituitary field needs conformal field shaping on a unit with 1.0 cm MLC leaves

d. In a large field, the distance between adjacent leaves exceeds the leaf length (e.g., 15 cm on some treatment units)

e. a cord block is added to a supraclavicular field

71. Cumulative dose volume histograms can show all of the following except:

a. the dose homogeneity over the PTV b. the maximum dose in an organ c. the percent of a contoured volume receiving a specific dose d. the location of the maximum tissue dose e. the minimum dose in an organ

72. Which factors influence the construction of a PTV from a CTV?

I. Patient set-up uncertainty II. organ motion

III. proximity of critical structure IV. extent of microscopic disease

a. 1, 2, 3 b. 1, 3 c. 2, 4 d. 4 only e. 1, 2, 3, 4

73. IMRT using MLC usually requires an increased number of MUs

compared with conventional RT because: a. of increased leakage through the MLC compared with cut

blocks b. a fraction of the treatment field is blocked at any given time c. IMRT is usually delivered with lower energy photons d. field margins are usually smaller

74. All of the following are true of IMRT except: a. IMRT dose distributions are always more inhomogeneous than

conventional 3D plans b. in prostate treatment, IMRT can reduce rectal toxicity c. a 3 data set is required for IMRT planning d. immobilization is more important because of tighter margins

75. It is recommended that the dose to a pacemaker be kept below 2.0 Gy.

In a lung treatment of 40 Gy with 10 MV photons, the fields should be no closer than ____ to the pacemaker.

a. 5 m b. 2 cm c. 7 cm d. 10 cm

76. The approximate maximum dose to a patient’s contralateral breast

from tangential breast fields treated with conventional wedges, and delivering a total dose of 5000 cGy is of the order of:

a. 2500 cGy b. 250 cGy c. 25 cGy d. 5 cGy e. negligible

77. Compared with linac-based SRS, treatment on the Gamma knife is

likely to result in ____ dose inhomogeneity across the target volume. a. greater b. less c. the same

78. The average primary transmission for 6 MV x-rays through a tertiary

MLC is about: a. 0.1 % b. 0.5 % c. 2 % d. 5 % e. 10 %

79. In an IMRT plan, the physician requests that 95% of the PTV be covered by 95% of the prescribed dose, with the maximum not to exceed 105%. A plan is created with only 85% covering 95% of the volume. Possible reasons include all of the following except:

a. the PTV is drawn to include part of the build-up region b. field heights have insufficient margin around the PTV c. the photon energy is too low d. the PTV abuts a region to be avoided, which has been given

high priority

80. Verification of “sliding window” IMRT plans can be performed by all of the following except:

a. hand calculation of the MU settings for each beam b. scanning films exposed in a phantom to each IMRT field c. software designed to independently calculate the MU for each

field d. diode arrays irradiated with the IMRT fields

81. IGRT can use a variety of imaging modalities at the time of treatment,

including 2D images using kV and MV sources. All of the following statement are true except:

a. kV images allow easier visualization of bones than MV images b. kV images look similar to DRRs generated with planning CTs c. kV images cause less artifacts from metal prostheses and dental

fillings than the MV images d. the kV images and detector must be carefully aligned to match

the geometry of the treatment (MV) beams

82. Decreasing CT slice thickness during Ct-simulation is useful in image-guided radiation therapy (IGRT) because:

I. of decreased CT dose to the patient II. less work is required for normal tissue contouring

III. inhomogeneity corrections are significantly more accurate IV. image quality of DRR improves

a. 1, 2, and 3 b. 1 and 3 c. 2 an 4 d. 4 only e. all are correct

83. For SRS performed on a Gamma Knife, the prescription level normally chosen is _____% of the maximum.

a. 100 b. 90 c. 80 d. 50

84. In the 3-field plan shown below, a homogeneous distribution can be

obtained in the PTV with either 45 or 60 wedges in the lateral fields. With 60 wedges, the relative weight of the open field would be ___ that in the 45 wedged plan.

a. greater than b. less than c. the same as

85. According to the DVH shown, all of the following are true except:

a. 100% of the volume receives at least 25% of the dose

b. 60% of the volume receives at least 75% of the dose

c. 50% of the volume receives at least 90% of the dose

d. 90% of the volume receives at least 50% of the dose

86. The dose distribution shown for breast tangents could be improved by _____.

a. using a larger wedge angle

b. inverting the direction of the wedges

c. using a smaller wedge angle

d. using a lower photon energy

e. both a and d

87. A treatment plan for tangential breast fields gives the isodose distribution shown in the sagittal and axial views. The dose distribution could be made more homogeneous by all of the following techniques except:

a. adding subfields with MLC to block the hot spot b. adding wedged fields with the thick end of the wedge inferior c. replacing the wedged fields with forward-planned IMRT fields d. increasing the wedge angle on the tangents

88. Which one of the following plans has the wedges in the correct orientation? C

89. The wedge angle that would give the most homogeneous distribution in the “wedged pair” in the diagram below is ___ degrees.

a. 10 b. 20 c. 30 d. 45 e. 60

90. Which of the following isodose patterns is consistent with the field configurations and wedges shown? D

91. Which of the following would make the isodose distribution more homogeneous?

a. increasing the wedge angle

b. using wider fields c. decreasing the wedge

angle d. adding the anterior field

92. The tangential fields in the diagram are angled so that their posterior borders are aligned. LAO gantry angle = 60°. Field width = 18cm (symmetrical) at 100 cm SAD. (Gantry angles are defined as: 0° = anterior; 90° = patient left; 180° = posterior; 270° = patient right). RPO Gantry angle = ____.

a. 240° + 5° b. 240° +10° c. 240° -5° d. 240° -10° e. 240° -20°

additional questions for review – 2d & 3d · 2019-09-20 · additional questions for review...

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