The in vitro colony assay: a predictor of clinical outcome

Purpose : To determine the predictive power of an in vitro colony assay on the clinical normal-tissue complication rate. Material and methods: Primary skin fibroblasts from 88 individuals were gen erated from the skin biopsies of patients who received a standardized radio therapy. Tissue was cultured for three to six passages, irradiated with dos es between 1 and 8 Gy under defined conditions, seeded and finally the colo nies were stained and counted after 10-14 days. The survival curves were fi tted by the L-Q model and the SF2, alpha/beta and plating efficiency were c alculated. Results: The parameters SF2 and plating efficiency were stable throughout t he 4-year test period. Intra-individual differences between repeated experi ments were significantly lower than inter-individual test results. For the observed acute skin and late normal-tissue reactions other than skin the in vitro parameter SF2 correlated significantly ( p < 0.005). For late skin r eactions this correlation was not found. Discussion : In contrast to other publications, a clear correlation was fou nd between the in vitro test results and clinically observed early reaction s. The lack of correlation for late skin reactions suggests that the combin ation of intrinsic radiation sensitivity and exogenous factors may alter th e clinically observed reaction of certain tissues to a different extent.