In vitro responses of R-1 and RUC-2 tumour cells to multiple dose fractionation and low dose rate irradiation

The experiments presented are part of a program in which the effectiveness of multiple daily fractionations and continuous irradiations at low dose rates on two tumour systems and on normal tissues have been investigated. Results of in vitro experiments with two tumour cell lines are presented. The efficacy of administering the total dose in multiple dose fractions or as continuous irradiation at a low dose rate as compared with acute single doses is evaluated. The two cell lines used were derived from a rat rhabdomyosarcoma, designated as R-1, and from a rat ureter carcinoma, coded as RUC-2. The fractions of surviving cells were determined by the colony formation assay after irradiations performed with 137Cs gamma sources. Fraction doses of 2.56 and 3.39 Gy and time intervals of 1, 2 or 3 h were used. A continuous dose rate of 0.3 Gyh-1 was used. The results indicate that both fractionation and low dose rate irradiation are less effective than irradiation given as acute single doses. It is possible with both R-1 and RUC-2 cells to obtain the same survival level with the same dose given either with multiple dose fractionation or low dose rate irradiation. (Auth.)