Deck 24: Photon Dose Distributions

Question 1

6)What are the appropriate wedges needed for beams with a hinge angle of 120 degrees?

A) 15 degree
B) 30 degree
C) 45 degree
D) 60 degree

Answer 1

B
If ø is the angle between the beams' central axes, called the hinge angle, and q is the wedge angle of the beams, then the relationship between the hinge and wedge angles that produces a uniform dose distribution is as follows:
ø = 180° - 2q or q = 90° = ø/2
Therefore, a hinge angle of 120 degrees would require a 30-degree wedge.

Question 2

16)In the convolution algorithm, primary fluence is represented by what symbol?

A) D(r)
B) y(r)
C) K
D) dV

Answer 2

B
The primary fluence, y(r), describes the primary dose that exists at the point r.

Question 3

12)Which of the following is the most favorable situation for the overall goal of radiation therapy?

A) Radiosensitive tumor and radiosensitive normal tissue
B) Radiosensitive tumor and radioresistant normal tissue
C) Radioresistant tumor and radioresistant normal tissue
D) Radioresistant tumor and radiosensitive normal tissue

Answer 3

B
When tumors are more radiosensitive than their surrounding normal tissues, a relatively high degree of tumor control may be achievable, at some given dose, with a reasonably low normal-tissue complication probability.

Question 4

14)Which type of IMRT treatment involves the "sliding window" technique?

A) "Step-and-shoot"
B) Dynamic MLC
C) "Tomotherapy"
D) Robotic IMRT

Question 5

2)Which of the following statements is false concerning beam profiles?

A) A beam profile describes radiation intensity as a function of position across the beam at a given depth.
B) A beam profile depicts the beam's intensity in a direction perpendicular to the beam's direction.
C) A beam profile is another one-dimensional spatial representation of the variation of beam intensity.
D) A beam profile is characterized by a continuous and gradual decrease in beam intensity.

Question 6

1)What is (are)spatial representation(s)of the magnitude of the dose produced by a source of radiation?

A) Treatment planning
B) Dose distributions
C) Dose calculation matrix
D) Dose-volume histogram (DVH)

Question 7

9)Beam attenuation in energy ranges typically used in radiation therapy is primarily the result of which type of interaction?

A) Compton scatter
B) Photoelectric effect
C) Pair production
D) All are equal

Question 8

5)What determines the hinge angle?

A) The angle between two beams' central axes that share an isocenter
B) The angle of the 80% isodose line with a line perpendicular to the central axis of a wedges field
C) The angle of the 100% isodose line with a line perpendicular to the central axis of a wedges field
D) The wedge angle divided by 2

Question 9

4)What is the most common field arrangement used in radiation therapy?

A) Single field
B) Parallel-opposed
C) Four-field box
D) Wedged-pair

Question 10

18)Which of the following accounts for target motion and uncertainty in positioning?

A) GTV
B) CTV
C) PTV
D) Treated volume

Question 11

10)In which tissue heterogeneity correction method are both the field size and the depth "scaled" to account for the presence of heterogeneities?

A) Power law TAR method
B) Generalized Batho correction
C) Equivalent TAR method
D) Delta volume method

Question 12

15)During IMRT treatments, how is the intensity of the beam altered?

A) Insertions of a wedge
B) Movement of the collimators
C) Movement of the MLCs
D) Fluctuations in beam energy

Question 13

3)What determines the wedge angle?

A) The angle of the 100% isodose line with a line perpendicular to the central axis
B) The actual measurements of the wedge
C) The angle of the 80% isodose line with a line perpendicular to the central axis
D) Two times the hinge angle

Question 14

19)Which of the following imitates a radiograph by reconstructing the diverge-corrected patient anatomy from the CT data set?

A) BEV
B) DVH
C) DRR
D) REV

Question 15

11)In which tissue heterogeneity correction method are primary and scatter separated?

A) Power law TAR method
B) Generalized Batho correction
C) Equivalent TAR method
D) Delta volume method

Question 16

13)Which type of intensity-modulated radiation therapy treatment delivery has the gantry in a fixed position with an initial multileaf collimators (MLC)pattern?

A) "Step-and-shoot"
B) Dynamic MLC
C) "Tomotherapy"
D) Robotic IMRT

Question 17

17)Which of the following is the palpable, visible, or demonstrable extent and location of malignant growth and is the volume of known disease?

A) GTV
B) CTV
C) PTV
D) Treated volume

Question 18

7)Which of the following factors can be corrected to adjust the isodose lines of beams with oblique incidences?
I)PDD
II)TAR
III)TMR

A) I and II
B) I and III
C) II and III
D) I, II, and III

Question 19

20)Which of the following is a plot of target or normal structure volume as a function of dose?

A) BEV
B) DVH
C) DRR
D) REV

Question 20

8)In the effective source-skin distance method and TAR method of correcting isodose curves for oblique incidence, what does the factor h represent?

A) Inverse square correction
B) Depth
C) Tissue deficit or excess
D) Source-skin distance, tissue-air ratio, or tissue-maximum ratio

Question 21

23)The process of identifying structures, target volumes, or normal tissues, by creating contours around them, is often called _____________________.

A) organ segmentation
B) virtual simulation
C) intensity modulation
D) heterogeneity correction

Question 22

24)The internal target volume (ITV)is the __________.

A) GTV + CTV
B) CTV + IM
C) PTV - GTV
D) ITV + SM

Question 23

22)The percent depth dose curve (PDD)is a representation of dose variation in __________ dimensions.

A) one
B) two
C) three
D) four

Question 24

21)At what point does the treatment planning process begin?

A) Dose determination
B) Beam delineation
C) Organ segmentation
D) CT imaging