FRCR Radiobiology

Question 1

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

Accepted Answer

1–3 Gy

Answer

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

Question 2

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

Accepted Answer

G2/M phase

Answer

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

Question 3

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

Accepted Answer

Double-strand breaks

Answer

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

Question 4

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

Accepted Answer

2.5–3.0

Answer

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.

Question 5

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

Accepted Answer

The difference between tumor control probability and normal tissue complication probability

Answer

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

FRCR - Fellowship of the Royal College of Radiologists Practice Test

FRCR - Fellowship of the Royal College of Radiologists Practice Test

FRCR Radiobiology