a. For differentiated cells that do not proliferate, e.g. nerve and muscle cells, "cell death" means the loss of a specific function.
b. A cell that has retained its reproductive integrity and can proliferate indefinitely to produce a colony is said to be "clonogenic".
c. For proliferating cells, e.g. stem cells, "cell death" means that the cell ceases to be clonogenic.
d. The purpose of radiotherapy is to cause the tumour cells to lose most of their functions, while still being clonogenic.
a. The relationship between the radiation dose and the number of cells that have gone through one mitosis after irradiation.
b. The relationship between the radiation dose and the proportion of cells that remain clonogenic.
c. The relationship between the radiation dose and the number of cells that have not suffered the loss of a specific function.
d. The relationship between the radiation dose and the proportion of cells that can produce DNA.
a. Apoptosis, i.e. programmed cell death, which also occurs in normal tissues.
b. Mitotic death, when the cell dies while attempting to divide, the reason being chromosomal aberrations.
a. A double-strand break in the DNA means that the chromatid breaks.
b. Two chromatid breaks are required to produce an asymmetric chromosomal aberration, such as a dicentric or a ring.
c. Cells that have an asymmetric chromosomal aberration die.
d. At low doses, the two chromatid breaks are caused by the passage of one charged particle, i.e. they have an occurence probability that is linearly proportional to the dose.
e. At high doses, the two chromatid breaks are caused by the passage of two charged particles, i.e. they have an occurence probability that is proportional to the square of the dose.
f. Points (d) and (e) above account for the linear-quadratic shape of the dose-effect curve and of the cell survival curve.
g. As the dose increases, the probability that the two chromatid breaks above will be caused by the same particle increases.
a. For sparsely ionizing radiations, the survival curve is initially linear (on a log-linear plot) and subsequently bends at higher doses.
b. For densely ionizing radiations, the survival curve is linear (on a log-linear plot) at all dose values which are relevant to radiotherapy.
c. The survival curves of various cell types have the same value of D0.
d. If many persons are studied, we see that the D0 values of various tumour cells vary over a wider interval than in the case of normal tissues.
e. Certain tumour cells are more radiosensitive than normal tissue cells, whereas others are more radioresistant.
a. Mitotic cells from various cell lines have different radiosensitivities.
b. The radiosensitivity of a cell line is proportional to the size of the shoulder of the its survival curve.
c. The more radiosensitive the cell line, the more important the contribution of apoptosis is.
a. "Multifraction regimen" means that the dose is delivered to the patient in a series of equal fractions, which are separated by time intervals that allow the repair of sublethal cell damage to take place.
b. Multifraction regimens in radiotherapy require the use of "effective dose survival curves".
c. The effective dose survival curve is an exponential function of the dose.
d. The dose required to kill 10% of all cells is called D0.