Radiobiology Flashcards

According to the linear-quadratic model, what is the typical alpha/beta ratio for late-responding normal tissues?

Answer: 1–3 Gy

Late-responding tissues have a low α/β ratio of ~1–3 Gy, making them more sensitive to high doses per fraction.

Which phase of the cell cycle is most sensitive to ionizing radiation?

Answer: G2/M phase

G2/M phase cells have the highest radiosensitivity because they have limited time for DNA repair before cell division.

What type of DNA damage is most responsible for radiation-induced cell death?

Answer: Double-strand breaks

Double-strand breaks are the most lethal form of radiation-induced DNA damage because they are difficult for cells to repair accurately.

The oxygen enhancement ratio (OER) for low-LET radiation such as X-rays is approximately:

Answer: 2.5–3.0

The OER for X-rays is approximately 2.5–3.0, meaning hypoxic cells require 2.5–3 times more dose to achieve the same cell kill as well-oxygenated cells.

Which of the following best defines the therapeutic ratio in radiotherapy?

Answer: The difference between tumor control probability and normal tissue complication probability

The therapeutic ratio represents the balance between tumor control probability (TCP) and normal tissue complication probability (NTCP), guiding optimal treatment dose selection.

According to the Bergonié and Tribondeau law, which cells are most radiosensitive?

Answer: Rapidly dividing, undifferentiated cells

Bergonié and Tribondeau established that cells are most radiosensitive when they are rapidly dividing, undifferentiated, and have a high mitotic rate.

In the linear-quadratic (LQ) model, the linear (α) component of cell kill represents:

Answer: Cell kill proportional to dose, representing lethal double-strand breaks from a single event

The α (linear) component represents cell kill proportional to dose, corresponding to a single lethal event such as a non-repairable double-strand break from one radiation track.