Modification of the effects of continuous low dose rate irradiation by concurrent chemotherapy infusion.

The combined effects of continuous low dose rate irradiation (CLDRI) and concurrent infusion of bleomycin, cyclophosphamide, cis-platinum, 5-fluorouracil, actinomycin D, and mitomycin C were studied in the SCC VII/SF tumor, a squamous cell carcinoma and the jejunal crypt cells in the mouse. For the SCC VII/SF tumor, enhanced cell killing was seen with each of the six drugs when infused concurrently with CLDRI; the greatest enhancement was seen with mitomycin C and cis-platinum. For the jejunal crypt cells, enhanced cell killing was seen primarily with bleomycin. At a dose of 20 Gy, the dose effect factor (DEF) ranged from 1.13-1.64 for the SCC VII/SF tumor and 0.92-1.19 for the jejunal crypt cells. Our results suggest a therapeutic gain with concurrent CLDRI and chemotherapy infusion for five of the six chemotherapeutic drugs studied with the exception of bleomycin.