Fraction size and the repair of potentially lethal radiation damage in a human melanoma cell line. Possible implications for radiotherapy.

Studies performed on a human melanoma line in exponential growth showed radiation survival parameters similar to those of other tumors (n = 1.2, D0 = 151). In plateau-phase cultures, however, this tumor cell line was efficient in the repair of potentially lethal radiation damage, especially when large dose fractions were employed (there was a 48-fold recovery after 1,200 rad [12 Gy]). Thus, extrapolation from survival data generated only on exponentially growing cells may be misleading when determining the ultimate surviving fraction in some tumors. Large-fraction radiotherapy may not be effective in tumors that contain cells analogous to plateau-phase cells.