CMD Radiation Physics & Radiobiology Flashcards
6 cards from real CMD practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 CMD Radiation Physics & Radiobiology flashcards as text
What is the unit of absorbed dose in the SI system used in radiation therapy dosimetry?
Answer: Gray (Gy)
The Gray (Gy) is the SI unit of absorbed dose, defined as 1 joule of energy deposited per kilogram of matter.
Which interaction of radiation with matter is most responsible for the biological damage caused by therapeutic X-rays?
Answer: Compton scattering
Compton scattering dominates at therapeutic energies (1–25 MV), producing energetic recoil electrons that cause ionization and biological damage.
In radiobiology, what does the 'α/β ratio' characterize?
Answer: Tissue sensitivity to fractionation
The α/β ratio describes how sensitive a tissue is to changes in fraction size; low α/β tissues (≈3 Gy) are more sensitive to large fractions.
What is the approximate half-value layer (HVL) concept used to characterize in radiation therapy physics?
Answer: Beam quality and penetrating power
The HVL is the thickness of a specified material that reduces beam intensity by 50%, characterizing the beam's penetrating ability and quality.
Which factor does the Tissue-Phantom Ratio (TPR) eliminate compared to Percent Depth Dose (PDD)?
Answer: Source-to-surface distance (SSD) dependence
TPR is measured at a fixed source-to-detector distance, making it independent of SSD and useful for isocentric treatment planning.
What radiobiological principle describes the repair of sublethal radiation damage between dose fractions?
Answer: The '4 Rs' of radiobiology — Repair
Repair of sublethal damage is one of the '4 Rs' of radiobiology and is the primary rationale for delivering radiation in multiple fractions over time.