CMD Treatment Planning & Dosimetry 3

Question 1

The tissue-maximum ratio (TMR) is preferred over the tissue-air ratio (TAR) for high-energy photon beams because:

Accepted Answer

TAR requires impractically large phantom measurements at high energies

Answer

At high photon energies, measuring TAR requires enormous phantoms to achieve electronic equilibrium at depth, making TMR with scatter factors more practical.

Question 2

Which contouring structure type is used in treatment planning to expand a target volume to account for subclinical disease extension?

Accepted Answer

Clinical Target Volume (CTV)

Answer

The CTV expands the GTV to include areas of suspected microscopic disease extension, representing the true anatomical extent of disease requiring treatment.

Question 3

In 4D CT-based treatment planning for lung cancer, the Internal Target Volume (ITV) is derived by:

Accepted Answer

Taking the union of GTVs contoured across all respiratory phases

Answer

The ITV is the union of all phase-specific GTVs across the breathing cycle, encompassing the full range of tumor motion.

Question 4

A symmetric 4-field box technique for prostate treatment typically uses which beam arrangement?

Accepted Answer

AP, PA, right lateral, left lateral

Answer

The classic 4-field box for prostate uses anterior-posterior, posterior-anterior, and bilateral lateral beams to distribute dose and spare anterior normal tissue.

Question 5

Which effect describes the increase in relative biological effectiveness (RBE) of radiation as linear energy transfer (LET) increases?

Accepted Answer

High-LET radiation reduces the oxygen enhancement ratio and increases RBE simultaneously

Answer

High-LET radiation both increases RBE (more lethal per unit dose) and reduces the oxygen enhancement ratio (less dependent on oxygen for cell kill).

(CMD) Certified Medical Dosimetrist Practice Test

(CMD) Certified Medical Dosimetrist Practice Test

CMD Treatment Planning & Dosimetry 3