[Experimental studies concerning comparison of the effect on the intestine between antitumor agents and radiation]

Though radiotherapy combined with chemotherapy is used increasingly more frequently in the recent treatment of malignant tumors, very little is known about what dose of an antitumor agent equals what radiation dose in effect. We tried to determine those radiation doses which are required to produce the same effect as certain specific doses of antitumor agents (isoeffective dose) by studying the early effects of radiation and drugs chiefly on the intestine of dd strain mice. Parameters used were food consumption, body weight change, 3H-TdR radioactivity in the intestine and the labelling index of intestinal crypt cells. The results were as follows: 1) To determine that radiation dose which is equal to a drug dose (1/2 its LD50) in systemic effect, body weight change and food consumption were suggested to be useful parameters. 2) To determine that radiation dose which is equal to a drug dose in the effect on a specific organ, parameters suitable for the target cells must be selected. For evaluating the effect on the intestine, the labelling index of intestinal epithelium was a useful parameter. 3) The results of treatment with combined radiation and slight amounts of drugs suggested that the degree of aggravation of radiation injury due to drugs might vary with the time of drug administration. 4) Graphic representation of the severity of injury as indicated by parameters enabled us to grasp visually the characteristics of drugs.