[Preoperative radiotherapy in rectal carcinoma. I. The effect of irradiation on the tumor volume].

We studied an effect of preoperative radiation upon the change of tumor volume in rectal carcinoma. As a preliminary study, tumor volume of 15 cases of rectal carcinoma with no preoperative irradiation was estimated preoperatively using the transrectal ultrasonography, and were compared with those determined by resected specimens after operation. As a result, there was a parallel relationship between the two values, and mean estimation error rate was 14.6%. Next, the same method was applied to 15 patients with rectal carcinoma who underwent preoperative radiation in order to detect the reduction rate of tumor volume after radiation therapy (42.6 Gy). As a consequence, 80% of cases exhibited the reduction rate more than 50% with an average of 61.7%. It was suggested that the determination of pre- and postoperative tumor volume would be beneficial to evaluation of preoperative radiation therapy as well as decision of the optimal dose of radiation in rectal carcinoma.