Radiation Physics & Radiobiology Flashcards
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Read the first 6 Radiation Physics & Radiobiology flashcards as text
The percentage depth dose (PDD) for a photon beam increases with:
Answer: Increasing beam energy and field size
PDD increases with higher beam energy (deeper penetration) and larger field size (more scatter contribution), both of which increase dose at depth relative to dmax.
Which radiobiological model is most commonly used in clinical dosimetry to compare different fractionation schedules?
Answer: Linear-Quadratic (LQ) model
The linear-quadratic model is the standard clinical tool for converting between fractionation schedules using the BED (Biologically Effective Dose) concept.
Inverse square law states that radiation intensity is proportional to:
Answer: 1/distance²
The inverse square law states that radiation intensity decreases with the square of the distance from a point source: I ∝ 1/d².
In brachytherapy, which quantity describes the strength of a radioactive source?
Answer: Air Kerma Strength (AKS)
Air Kerma Strength (U = μGy·m²/h) is the standard quantity for specifying brachytherapy source strength, replacing older activity-based specifications.
Which radiation type has the highest relative biological effectiveness (RBE) for clinical applications?
Answer: High-energy neutrons
High-energy neutrons have RBE values of 5–20 due to their high-LET nature, producing dense ionization tracks that cause more complex, irreparable DNA damage.
The therapeutic ratio in radiation therapy is optimized by:
Answer: Maximizing tumor cell kill while minimizing normal tissue damage
The therapeutic ratio is the relationship between tumor control probability (TCP) and normal tissue complication probability (NTCP), and is maximized through precise targeting and appropriate fractionation.