CMD Clinical Oncology & Treatment Techniques 1 — Questions and Answers
Question 1: Which imaging modality is most commonly used for radiation therapy simulation and treatment planning due to its electron density information?
- CT (Computed Tomography) (Correct answer)
- MRI
- PET scan
- Ultrasound
Correct answer: CT (Computed Tomography)
CT simulation provides Hounsfield unit data that is directly converted to electron density for dose calculation algorithms, making it the standard for treatment planning.
Question 2: In ICRU Report 62, which volume encompasses the Clinical Target Volume (CTV) plus a margin for setup uncertainty and organ motion?
- Planning Target Volume (PTV) (Correct answer)
- Gross Tumor Volume (GTV)
- Internal Target Volume (ITV)
- Organ at Risk (OAR)
Correct answer: Planning Target Volume (PTV)
The PTV adds a geometric margin around the CTV to account for setup uncertainties and internal organ motion, ensuring the CTV receives the prescribed dose.
Question 3: Which technique uses multiple non-coplanar arcs or beams with modulated intensity to deliver highly conformal dose distributions?
- Intensity-Modulated Radiation Therapy (IMRT) (Correct answer)
- 3D Conformal Radiation Therapy (3DCRT)
- Total Body Irradiation (TBI)
- Electron arc therapy
Correct answer: Intensity-Modulated Radiation Therapy (IMRT)
IMRT uses computer-optimized, modulated beam intensities across multiple fields to create dose distributions that conform tightly to target volumes while sparing adjacent critical structures.
Question 4: For breast cancer radiation therapy, the tangential field technique is designed primarily to:
- Treat the breast/chest wall while minimizing lung and heart dose (Correct answer)
- Cover all regional lymph nodes simultaneously
- Maximize skin dose
- Treat bilateral breast fields equally
Correct answer: Treat the breast/chest wall while minimizing lung and heart dose
Tangential fields are angled to treat the breast/chest wall volume while minimizing the dose to underlying lung and, for left-sided cancers, the heart.
Question 5: Which dosimetric parameter is most critical to monitor when treating head and neck cancers with IMRT to prevent xerostomia?
- Mean parotid gland dose (Correct answer)
- Maximum spinal cord dose only
- Minimum PTV dose
- V95 of the mandible
Correct answer: Mean parotid gland dose
Mean parotid gland dose should ideally be kept below 26 Gy to at least one parotid to preserve salivary function and prevent permanent xerostomia.
Question 6: Stereotactic Radiosurgery (SRS) is characterized by:
- High dose per fraction, few fractions, and submillimeter precision (Correct answer)
- Conventional fractionation over 5–6 weeks
- Large treatment volumes with uniform dose
- Multiple isocenters all treated over many fractions
Correct answer: High dose per fraction, few fractions, and submillimeter precision
SRS delivers ablative doses (typically 12–24 Gy) in 1–5 fractions using stereotactic immobilization and multiple converging beams to achieve submillimeter targeting accuracy.
CMD Clinical Oncology & Treatment Techniques 1
Which imaging modality is most commonly used for radiation therapy simulation and treatment planning due to its electron density information?