CMD CMD Clinical Oncology & Disease Sites 2 — Questions and Answers
Question 1: In cervical cancer brachytherapy combined with EBRT, what dose fractionation is commonly used for the EBRT component?
- 45–50 Gy in 25 fractions to the pelvis (Correct answer)
- 60–70 Gy in 30–35 fractions
- 20 Gy in 5 fractions (SBRT)
- 70 Gy in 35 fractions with concurrent chemotherapy
Correct answer: 45–50 Gy in 25 fractions to the pelvis
Standard pelvic EBRT for cervical cancer is 45–50 Gy in 25 fractions (1.8 Gy/fraction), typically combined with concurrent cisplatin chemotherapy and intracavitary brachytherapy.
Question 2: What treatment technique is commonly used for whole-brain radiation to reduce dose to the lens of the eye?
- Angling beams posteriorly to exclude the lens
- Using IMRT to spare the lens
- Applying a lens block or cerrobend shield (Correct answer)
- Reducing total prescription dose
Correct answer: Applying a lens block or cerrobend shield
Custom cerrobend blocks or multi-leaf collimator-based shielding are used to block the lens during WBRT, reducing cataract risk from lens doses.
Question 3: Which staging system is most commonly used for lung cancer to define target volumes in radiation therapy planning?
- AJCC TNM staging (Correct answer)
- FIGO staging
- Ann Arbor staging
- Dukes staging
Correct answer: AJCC TNM staging
The AJCC TNM (Tumor, Node, Metastasis) staging system defines primary tumor extent, nodal involvement, and metastatic status, directly informing target volume delineation for lung cancer.
Question 4: In stereotactic body radiation therapy (SBRT) for early-stage lung cancer, what is a commonly used fractionation regimen?
- 54 Gy in 3 fractions (18 Gy × 3) (Correct answer)
- 60 Gy in 30 fractions
- 45 Gy in 25 fractions
- 20 Gy in 1 fraction
Correct answer: 54 Gy in 3 fractions (18 Gy × 3)
54 Gy in 3 fractions (or 48–60 Gy in 3–5 fractions) is a standard SBRT regimen for peripheral early-stage NSCLC, achieving high local control rates comparable to surgery.
Question 5: What is the most common beam arrangement for treating a right-sided breast cancer with standard tangential fields?
- Medial and lateral tangents to minimize lung dose (Correct answer)
- AP/PA parallel-opposed fields
- Four-field box technique
- Single anterior oblique field
Correct answer: Medial and lateral tangents to minimize lung dose
Medial and lateral tangential fields bracket the breast tissue while minimizing the volume of lung and heart in the treatment field, particularly important for left-sided tumors.
Question 6: In rectal cancer radiotherapy, which structure must be particularly protected to minimize the risk of small bowel toxicity?
- Small bowel (loops within the pelvis) (Correct answer)
- Femoral heads
- Bladder only
- Spinal cord
Correct answer: Small bowel (loops within the pelvis)
Small bowel loops within the pelvis are highly radiosensitive; dosimetrists must minimize the volume receiving ≥45 Gy (V45 < 195 cc) to prevent acute and late bowel toxicity.
CMD CMD Clinical Oncology & Disease Sites 2
In cervical cancer brachytherapy combined with EBRT, what dose fractionation is commonly used for the EBRT component?