CMD Treatment Simulation & Immobilization 2

Question 1

Which type of CT acquisition is used to capture and characterize respiratory tumor motion during thoracic simulation?

Accepted Answer

4D-CT (four-dimensional CT)

Answer

4D-CT acquires images sorted by respiratory phase, enabling visualization of tumor motion throughout the full breathing cycle for lung and liver treatments.

Question 2

What does the Internal Target Volume (ITV) account for in radiation therapy planning?

Accepted Answer

Internal organ motion due to physiological processes such as respiration

Answer

The ITV encompasses the range of motion of the GTV/CTV caused by internal physiological movement, most commonly respiratory motion in thoracic and abdominal treatments.

Question 3

A Digitally Reconstructed Radiograph (DRR) is generated from:

Accepted Answer

CT simulation data using ray-tracing algorithms through the 3D volume

Answer

DRRs are synthetic radiographs computed by tracing rays through CT simulation volumetric data, used as reference images for image-guided patient setup verification.

Question 4

What is the primary advantage of vacuum-lock (vac-lock) bags compared to other immobilization devices?

Accepted Answer

They conform to any body contour and harden into custom-fitted, reproducible positioning aids

Answer

Vacuum bags conform to the patient's body surface and become rigid when air is evacuated, providing comfortable, custom-fitted immobilization adaptable to any treatment site.

Question 5

When using respiratory gating for lung SBRT, the treatment beam is delivered during:

Accepted Answer

A defined phase or amplitude range of the respiratory cycle

Answer

The gating window is a specific respiratory phase or amplitude range during which the beam is active, reducing the required PTV margin by treating only when the tumor is in a reproducible position.

(CMD) Certified Medical Dosimetrist Practice Test

(CMD) Certified Medical Dosimetrist Practice Test

CMD Treatment Simulation & Immobilization 2