Criteria and techniques for analysing cell survival data

Cell survival was studied by analyzing the inactivation probability density function and its fundamental parameters. Mean D, variance sigma 2 and mode Dmode were evaluated and a set of equations relating these parameters to the usual parameters of the multitarget, multihit and linear-quadratic models Do and n, alpha and beta, kappa and lambda are reported. The multihit equation used was an extension of the usual equation, to allow parameter kappa to assume values that are not necessarily integers. In the multitarget curve, the mode of inactivation probability density function, proved to be the quasi-threshold dose Dq = Do ln(n). Relative variance, degree of asymmetry and degree of peakedness can be calculated from the shape parameters n in the multitarget model, kappa in the multihit model, and alpha/square root of beta in the linear-quadratic model. From an analysis of eight published cell survival sets of data, on C3H10T1/2 cells exposed to low LET radiations, it was found that D, sigma, and SF2 are the parameters which exhibit the least variation from experiment to experiment and the least variation in selecting the range of data available for estimation.