Relationships between colony forming efficiency and parameters of intrinsic radiosensitivity

In an attempt to determine whether radiosensitivity is correlated with colony forming efficiency (CFE), a large amount of data have been analysed from the literature.

The survival curves of 446 human cell lines irradiated in exponentially growing phase in vitro are included in this study. Technical factors such as culture type and the use of feeder cells were considered cofactors in addition to the genetic and histological origin of the cells. Intrinsic radiosensitivity is expressed in terms of the parameters of the linear quadratic model and the single-hit multitarget model.

It is shown that low CFE is characteristic of cells plated in agar and cells from primary biopsies. Cells plated in the presence of feeder cells have, in general, higher CFE than cells plated without feeder cells. A positive correlation is observed between intrinsic radiosensitivity and CFE: the higher the CFE, the more resistant the cell line. This relationship is particularly obvious when radiosensitivity is expressed in terms of alpha, S2 or D, parameters which essentially characterize the initial part of the survival curve. The correlation is also found within histological or genetic groups of cell lines. However, for a given cell line, there is no relationship between CFE and radiosensitivity among different experiments. Cells irradiated in the presence of feeder cells are less subject to this behaviour.

CFE as well as radiosensitivity are intrinsic properties of a cell line. Experimental conditions determine the quality of the correlation between radiosensitivity and CFE.