The influence of time sequence of cisplatin administration and continuous low dose rate irradiation (CLDRI) on their combined effects on a murine squamous cell carcinoma.

The influence of time sequence of cis-dichlorodiammine platinum (cisplatin) administration and continuous low dose rate irradiation (CLDRI) on their combined effects was studied in the SCC VII/SF tumor, a murine squamous cell carcinoma. Concurrent cisplatin i.p. infusion at 0.22 mg/kg/hr and CLDRI at 0.6 Gy/hr had a supraadditive effect on the survival of the SCC VII/SF tumor cells. Cisplatin by itself was more effective against the SCC VII/SF tumor when given by bolus injection than by continuous infusion i.p. However, when cisplatin at a dose of 6 mg/kg was given by bolus i.p. injection either immediately before or after CLDRI, the combined effects on the SCC VII/SF tumor cell survival were no more than additive. Exposure to CLDRI at 0.6 Gy/hr for 24 hours did not sensitize the SCC VII/SF tumor to subsequent treatment with cisplatin. These results suggest that when cisplatin is combined with CLDRI, for the optimal anti-tumor effect, it is best to infuse the cisplatin continuously during the course of CLDRI.