Radiation Biology Flashcards

Compared to low-LET radiation, high-LET radiation has a relative biological effectiveness (RBE) that is:

Answer: Higher — more biologically effective per unit dose

High-LET radiation has a higher RBE because its dense ionization tracks cause more complex, clustered DNA damage that is more difficult to repair than the sparse ionization of low-LET photons.

In the linear-quadratic model S = e^(–αD – βD²), the αD (linear) component represents:

Answer: Single-hit (single-track) lethal cell killing

The αD linear component represents single-track, single-hit lethal events where one ionizing particle event causes an irreparable, lethal lesion proportional to dose.

What is 'reoxygenation' in the context of tumor radiobiology?

Answer: The re-establishment of oxygen supply to previously hypoxic tumor cells after irradiation

Reoxygenation occurs when previously hypoxic (radioresistant) tumor cells become oxygenated after a fraction kills well-oxygenated cells, making the surviving hypoxic cells more sensitive to subsequent fractions.

Which tissues have a LOW alpha/beta ratio of approximately 2–3 Gy?

Answer: Late-responding tissues such as spinal cord and lung

Late-responding tissues like spinal cord, lung, and kidney have low α/β ratios (~2–3 Gy), meaning they are particularly sensitive to large fraction sizes and benefit more from standard fractionation.

The Bergonié-Tribondeau law states that cells are MORE radiosensitive when they:

Answer: Have high mitotic activity and are less differentiated

The Bergonié-Tribondeau law (1906) states that cells with high mitotic activity, great proliferative future, and less differentiation are more radiosensitive — which is why cancer cells are generally more sensitive than mature normal cells.

What is 'sublethal damage repair' (SLDR) in radiobiology?

Answer: Repair of radiation-induced lesions that, if unrepaired, could accumulate into lethal damage

SLDR refers to the repair of DNA lesions (e.g., single-strand breaks) that are individually non-lethal but become lethal if combined with additional damage; this repair is the biological basis for the shoulder on cell survival curves.

What is the Tumor Control Probability (TCP) in radiation oncology?

Answer: The statistical likelihood that a given radiation dose will eradicate all clonogenic tumor cells

TCP is the probability that a specific radiation dose will sterilize every clonogenic (colony-forming) cell in the tumor, resulting in local control; it increases with dose in a sigmoidal relationship.