CELLULAR RADIOSENSITIVITY OF SMALL-CELL LUNG-CANCER CELL-LINES

Purpose: The objective of this study was to determine the radiobiologi cal characteristics of a panel of small-cell lung cancer (SCLC) cell l ines by use of a clonogenic assay. In addition, we tested whether comp arable results could be obtained by employing a growth extrapolation m ethod based on the construction of continuous exponential growth curve s. Methods and Materials: Fifteen SCLC cell lines were studied, applyi ng a slightly modified clonogenic assay and a growth extrapolation met hod. A dose-survival curve was obtained for each experiment and used f or calculating several survival parameters. The multitarget single hit model was applied to calculate the cellular radiosensitivity (D-o), t he capacity for sublethal damage repair (D-q), and the extrapolation n umber (n). Values for alpha and beta were determined from best-fit cur ves according to the linear-quadratic model and these values were appl ied to calculate the surviving fraction after 2-Gy irradiation (SF2). Results: In our investigation, the extrapolation method proved to be i nappropriate for the study of in vitro cellular radiosensitivity due t o lack of reproducibility. The results obtained by the clonogenic assa y showed that the cell lines studied were radiobiologically heterogene ous with no discrete features of the examined parameters including the repair capacity. Conclusion: The results indicate that SCLC tumors pe r se are not generally candidates for hyperfractionated radiotherapy. (C) 1997 Elsevier Science Inc.