RADIOSENSITIZATION BY IODO-DEOXYURIDINE IN CULTURED SW-1573 HUMAN LUNG-TUMOR CELLS - EFFECTS ON ALPHA AND BETA OF THE LINEAR-QUADRATIC MODEL

To investigate radiosensitization by halogenated pyrimidines in human cells, SW-1573 lung tumor cells were grown in absence or presence of 4 mu M of iododeoxyuridine (IdUrd). Cell survival after irradiation wit h gamma-rays from a Cs-137 source with single doses up to 8 Gy, was de termined by clonogenic assay, Radiosensitization by IdUrd was observed in both exponentially growing and plateau phase cells. Linear-quadrat ic analyses of the radiation survival curves demonstrated that radiose nsitization was mainly expressed by an increase of the value of alpha (determining the initial slope of the survival curve) which can be int erpreted as an enhancement of fixation of potentially lethal damage (P LD). The value of beta (determining the curvature of the survival curv e), which might be attributed to enhanced interaction or to fixation o f sublethal damage (SLD), was not influenced. In view of clinical appl ications of IdUrd it is of interest that radiosensitization has its ma in effect in the low dose region of the cell survival curve, described by the linear term alpha D.