CMD Radiation Physics & Radiobiology

Question 1

What is the unit of absorbed dose in the SI system used in medical dosimetry?

Accepted Answer

Gray (Gy)

Answer

Rad

Answer

Sievert (Sv)

Answer

Roentgen (R)

Question 2

Which concept describes the ability of ionizing radiation to cause DNA double-strand breaks relative to a reference radiation?

Accepted Answer

Relative Biological Effectiveness (RBE)

Answer

Oxygen Enhancement Ratio (OER)

Answer

Linear Energy Transfer (LET)

Answer

Therapeutic Ratio

Question 3

The oxygen enhancement ratio (OER) is highest for which type of radiation?

Accepted Answer

Low-LET radiation (X-rays, gamma rays)

Answer

Fast neutrons

Answer

Alpha particles

Answer

Heavy ions

Question 4

In the linear-quadratic (LQ) model, the α/β ratio for late-responding normal tissues is typically:

Accepted Answer

2–3 Gy

Answer

8–10 Gy

Answer

15–20 Gy

Answer

0.5–1 Gy

Question 5

Which physical process is dominant for photon interactions in tissue at megavoltage energies used in radiation therapy?

Accepted Answer

Compton scattering

Answer

Photoelectric effect

Answer

Pair production

Answer

Rayleigh scattering

Question 6

The depth of maximum dose (dmax) for a 6 MV photon beam in water is approximately:

Accepted Answer

1.5 cm

Answer

0.5 cm

Answer

3.0 cm

Answer

5.0 cm