CMD Treatment Simulation & Immobilization 1 — Questions and Answers
Question 1: What is the primary purpose of CT simulation in radiation therapy treatment planning?
- To diagnose the primary cancer site
- To define the patient's 3D anatomy and establish treatment geometry (Correct answer)
- To deliver the first fraction of radiation
- To assess tumor response after treatment
Correct answer: To define the patient's 3D anatomy and establish treatment geometry
CT simulation provides volumetric anatomical data necessary for target volume delineation, beam arrangement, and dose calculation in treatment planning.
Question 2: Which immobilization device is most commonly used for head and neck cancer treatments?
- Vacuum-lock bag
- Thermoplastic mask (Correct answer)
- Alpha cradle
- Wing board
Correct answer: Thermoplastic mask
Thermoplastic masks are custom-molded to the patient's facial contour and harden at room temperature, providing reproducible immobilization for head and neck treatments.
Question 3: What is the recommended CT slice thickness for treatment planning of head and neck tumors?
- 10 mm
- 5 mm
- 3 mm or less (Correct answer)
- 15 mm
Correct answer: 3 mm or less
Slice thicknesses of 3 mm or less provide superior anatomical detail for delineating complex structures in the head and neck region and improve dose-volume histogram accuracy.
Question 4: What is the purpose of using a flat couch insert during CT simulation?
- To reduce radiation dose to the patient during scanning
- To match the flat treatment couch geometry for consistent patient positioning between simulation and treatment (Correct answer)
- To improve CT image quality by reducing scatter
- To decrease the total scan time
Correct answer: To match the flat treatment couch geometry for consistent patient positioning between simulation and treatment
A flat couch insert replicates the flat linac treatment couch surface so the patient geometry at simulation matches treatment delivery conditions.
Question 5: Which patient preparation protocol is typically followed during prostate cancer CT simulation to reduce normal tissue dose?
- Prone position with empty bladder
- Supine position with full bladder and empty rectum (Correct answer)
- Left lateral decubitus with Foley catheter
- Trendelenburg position with oral contrast only
Correct answer: Supine position with full bladder and empty rectum
A full bladder displaces the small bowel superiorly out of the treatment field while an empty rectum minimizes rectal volume receiving high dose.
Question 6: What is the primary function of intravenous (IV) contrast during CT simulation?
- To improve patient comfort during scanning
- To enhance visualization of blood vessels and tumor boundaries for target delineation (Correct answer)
- To reduce imaging artifacts from metallic implants
- To minimize radiation exposure to the patient
Correct answer: To enhance visualization of blood vessels and tumor boundaries for target delineation
IV contrast enhances hypervascular tissues and blood vessels, helping to distinguish tumor margins from surrounding normal anatomy during target volume delineation.
Question 7: Radio-opaque BB markers placed on a patient's skin during CT simulation serve what primary purpose?
- To improve CT image resolution
- To mark reference or isocenter locations visible on CT images for planning and tattoo placement (Correct answer)
- To track respiratory motion during scanning
- To verify CT scanner calibration accuracy
Correct answer: To mark reference or isocenter locations visible on CT images for planning and tattoo placement
BBs appear as bright high-density objects on CT images, allowing the dosimetrist to identify the precise anatomical location of planned isocenter or reference marks.
CMD Treatment Simulation & Immobilization 1
What is the primary purpose of CT simulation in radiation therapy treatment planning?