Is dose/time fractionation important in treating rectal cancer?

In a study to evaluate the effect of increasing dose per fraction on radiation response in rectal cancer, two groups of 29 patients each, matched for extent and size of disease, were evaluated. Group A was treated with conventional dose/fraction (180-200 cGy) X 5 days/week and Group B was treated with 250 cGy/fraction X 4 days/week. Total dose was reduced by 10% in Group B patients to allow comparison of biologically equivalent doses. Two categories of patients were analyzed in each group: patients receiving planned high dose preoperative radiation (4000-4500 cGy); and patients receiving high dose radiation for post-surgical recurrent tumors or locally advanced inoperable tumors (5500-6000 cGy). Tumor regression was markedly better in patients treated with the 250 cGy/fraction. Overall response (greater than 50% regression) was 35% (10/29) in Group A and 62% (18/29) in Group B. Nine of 10 patients in Group B, treated preoperatively, had greater than 50% regression in tumor size, with two patients having no evidence of disease on surgico-pathological evaluation. Six of 10 similar patients in Group A had greater than 50% tumor regression.