RT Radiation Biology 2

Question 1

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

Accepted Answer

Higher — more biologically effective per unit dose

Answer

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.

Question 2

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

Accepted Answer

Single-hit (single-track) lethal cell killing

Answer

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

Question 3

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

Accepted Answer

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

Answer

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.

Question 4

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

Accepted Answer

Late-responding tissues such as spinal cord and lung

Answer

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.

Question 5

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

Accepted Answer

Have high mitotic activity and are less differentiated

Answer

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.

RT - Radiation Therapist Certification Practice Test

RT - Radiation Therapist Certification Practice Test

RT Radiation Biology 2