Solid tumor models for the assessment of different treatment modalities: systematics of response to radiotherapy and chemotherapy.

The change of tumor volumes (efficiency) with local tumor radiation doses from 375R to 3750R and 5-fluorouracil (5-FUra) from 50 to 250 mg/kg was assessed in rats bearing hepatoma 3924A. The data were analyzed utilizing a chi2 technique which fits the logarithmic volume response to polynomials. This provided greater flexibility in selecting different mathematical forms, and allows more accurate description of tumor changes after treatment than the least squares analysis previously used. Quantitative information can be obtained on one tumor following treatment by this method. This information is more analogous to the management of a patient with a solid tumor. The results show a continuous increase in efficiency of radiation throughout the radiation dose range from 375R to 3750R. The efficiency of 5-FUra increased slightly but did not continue to increase with doses of 5-FUra higher than 150 mg/kg. This suggests that factors such as toxicity to the host may prevent further increases of the effectiveness of 5-FUra. The time of minimum tumor volume change after radiation was approximately 6 days and for 5-FUra, 6 days. The time for maximum tumor volume change for 5-FUra was 12 days. There was a slight trend upward for maximum growth for increasing radiation doses from 18 to 22 days. The time of occurrence of both minimum and maximum tumor volume change after treatment showed little relationship to increasing doses of radiation and 5-FUra. Parallel studies have shown that the maximum rate of tumor volume change occurs shortly after the recovery of the host from the effect of 5-FUra. It is feasible, therefore, to use chemotherapy alone or in combination with radiotherapy, and optimize the scheduling of these treatment modalities with recovery of the host from previous therapy.