CMD Clinical Oncology & Treatment Techniques 2

Question 1

The dose-volume histogram (DVH) type that shows the percentage of a structure volume receiving at least a given dose is called:

Accepted Answer

Cumulative (integral) DVH

Answer

The cumulative DVH plots the fractional volume of a structure receiving at least a specified dose and is the standard format for evaluating treatment plans against dose-volume constraints.

Question 2

Which organ at risk constraint is commonly applied for the spinal cord in radical radiation therapy to prevent radiation myelopathy?

Accepted Answer

Maximum point dose ≤ 45–50 Gy in conventional fractionation

Answer

The spinal cord maximum dose is typically limited to 45–50 Gy in conventional fractionation to maintain the risk of radiation myelopathy below 0.2%.

Question 3

In prostate cancer treatment planning, which normal tissue constraint is used to reduce the risk of rectal bleeding?

Accepted Answer

Rectal V70 < 20% (volume of rectum receiving 70 Gy)

Answer

Limiting the rectal V70 to less than 20% reduces the risk of late rectal toxicity, including rectal bleeding, following definitive prostate radiotherapy.

Question 4

The electron beam depth dose characteristic known as the 'practical range' (Rp) is used to:

Accepted Answer

Estimate the maximum depth of electron beam penetration in tissue

Answer

The practical range Rp represents the depth beyond which the electron dose falls to near zero and is used to select appropriate electron beam energy for target coverage.

Question 5

Which beam arrangement is used in total body irradiation (TBI) to achieve dose uniformity across the entire patient?

Accepted Answer

Bilateral extended-SSD fields with compensators or lung blocks

Answer

TBI uses extended SSD bilateral fields with tissue compensators and partial lung blocks to achieve ±10% dose homogeneity across the heterogeneous patient anatomy.

(CMD) Certified Medical Dosimetrist Practice Test

(CMD) Certified Medical Dosimetrist Practice Test

CMD Clinical Oncology & Treatment Techniques 2