1. Radiation damage is divided into (a) lethal damage, (b) sublethal damage and (c) potentially lethal damage (PLD). Which of the following statements is true?

a. PLD will cause cell death under ordinary circumstances.

b. PLD cannot be repaired under ordinary circumstances.

c. The variation of postirradiation conditions cannot enhance PLD repair.

d. Mitosis cannot be delayed by suboptimal growth conditions.

e. PLD repair is less likely to occur when mitosis is delayed.

2. By "sublethal damage" is meant:

a. an irreversible damage which leads to cell death.

b. an irreversible damage which does not always lead to cell death.

c. a damage that can be repaired unless it interacts with a subsequently induced sublethal damage.

d. a damage that can be modified by postirradiation environmental conditions.

3. Sublethal damage repair is:

a. connected to PLD repair.

b. responsible for the radioresistance of certain types of tumours.

c. the reason for the increase in cell survival which is observed when a radiation dose is split into two fractions separated by a time interval.

d. continuously enhanced as the time interval between the two dose fractions mentioned in answer c is increased.

4. The increase of cell survival because of sublethal damage repair:

a. is not affected by the cell cycle.

b. is hindered by the increase in radiosensitivity as the cells progress around the cell cycle ("reassortment").

c. has no connection to cell synchronization.

d. is not enhanced by cell division ("repopulation").

5. Which of the following statements is true?

a. The strong variations in the cell survival curve which are due to reassortment and repopulation are observed in the case of rapidly growing cells as well as in the case of slowly growing cells.

b. Sublethal damage repair is a process which is not affected by the presence of oxygen and nutrients.

c. In a fractionated dose regimen, increase in cell survival occurs because the shoulder of the cell survival curve is repeated every time a dose is delivered.

d. Sublethal damage repair accounts for the increase in cell survival in a split-dose case for all time intervals between dose fractions.

e. There is no correlation between the extent of sublethal damage repair and the size of the shoulder of the acute survival curve.

f. Sublethal damage repair is completed within 1 to 2 hours both for cells in culture and for tissues in vivo.

6. Which of the following statements is true?

a. Sublethal damage repair consists in the repair of double-strand breaks.

b. Dose fractionation affects the cell killing component which is due to double-strand breaks produced by single-track damage.

c. The amount of sublethal damage repair does not vary with the type of radiation.

d. Sublethal damage repair is not significant in the case of x-rays.

7. The dose-rate effect:

a. is not important in radiotherapy.

b. does not affect significantly the biologic effect of x-rays or gamma rays.

c. consists in the reduction of the biologic effect of a given dose when the exposure time is increased.

d. is not due to sublethal damage repair.

e. has a magnitude that does not depend on cell type.

f. is not affected by cell proliferation.

8. Which of the following statements is true?

a. Cells with a small shoulder in the cell survival curve exhibit a strong dose-rate effect.

b. The dose-rate effect is most important at low doses.

c. The dependence on cell type both of the size of the shoulder in the acute survival curve and of the magnitude of the dose-rate effect are related to the significance of apoptosis for the specific cell type.

d. When different cell types are compared, their inherent radiosensitivity is shown in the survival curves obtained at low dose rates rather than high dose rates.

e. At high dose rates, the difference between survival curves of different cell types is enhanced by the variation with cell type of the sublethal damage repair time.

9. The inverse dose-rate effect is evident in a given interval of dose rates and is due to the fact that, within this given interval, cells are "frozen" in the phase of the cell cycle they are in at the beginning of the irradiation in the case of high dose rates; at low dose rates, cells continue to cycle during irradiation.

a. True.

b. False.