Deck 25: Photon Dose Distributions

Question 1

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.

Answer 1

D
They are characterized by a rapid increase in intensity (as the radiation detector enters the beam),followed by a region of relatively uniform intensity (characterizing the central portion of the beam),then ending with a rapid decrease in intensity (as the detector exits the beam).

Question 2

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 2

B
If ø is the angle between the beams' central axes,called the hinge angle,and  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° - 2 or  = 90° = ø/2
Therefore,a hinge angle of 120 degrees would require a 30-degree wedge.

Question 3

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

Answer 3

D
All factors listed can be corrected.

Question 4

The Bentley-Milan algorithm is an example of which type of treatment planning algorithm?

A) data-driven algorithms
B) scatter integration algorithms
C) model-driven algorithms
D) convolution algorithms

Question 5

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 6

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

A) D(r)
B) $\varPsi$ (r)
C) K
D) dV

Question 7

In the effective SSD 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) SSD,TAR,or TMR

Question 8

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 9

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

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

A) "step-and-shoot"
B) dynamic MLC
C) "tomotherapy"
D) robotic IMRT

Question 11

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 12

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 13

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

Question 14

Which type of IMRT treatment delivery has the gantry in a fixed position with an initial MLC pattern?

A) "Step-and-shoot"
B) dynamic MLC
C) "tomotherapy"
D) robotic IMRT

Question 15

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 16

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

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

Question 17

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) 2 times the hinge angle

Question 18

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 19

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 20

Which of the following is the palpable,visible,and/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 21

The desired outcome in radiation oncology is a high degree of tumor control with minimal deleterious side effects.

Question 22

Effective SSD and TAR methods of correcting for tissue heterogeneities result in accurate isodose distributions.

Question 23

Organ segmentation is the process of identifying structures,target volumes,or normal tissues,by creating contours around them.

Question 24

Each point along an isodose line has exactly the same dose.

Question 25

The flattening filter is designed to produce a "flat" intensity pattern throughout the beam profile.

Question 26

At what point does the treatment planning process begin?

A) dose determination
B) bean delineation
C) organ segmentation
D) CT imaging

Question 27

The percentage depth dose (PDD)curve is an example of a two-dimensional representation of the variation of dose.

Question 28

The 3DCRT method uses conventional inverse planning.

Question 29

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 30

Critical structures are contoured for intensity modulated radiation therapy (IMRT)planning but not for 3DCRT planning.