Dose-response relationship for radiation therapy of recurrent, residual, and primarily inoperable colorectal cancer.

One hundred and thirteen patients with advanced locoregional recurrent (77), residual (18) or primarily inoperable (18) colorectal carcinoma were treated with radiotherapy. Eighty-five patients had locoregional disease only and 28 had both local disease and distant metastases. The treatment was given with varying dose levels (23-73 Gy) in daily fractions of approximately 2 Gy in 3-8 weeks. This dose variation allowed an evaluation of the dose-response relationship for radiation treatment of this tumour. A good subjective response was obtained in 63%. This effect showed no dose-response relationship except for doses greater than or equal to 56 Gy, where all patients received relief of symptoms. Eighty-two per cent of evaluable patients achieved an objective response (PR 53%, CR 29%). The frequency and duration of the complete responses showed a marked dose-response relationship. Thus, at doses greater than or equal to 56 Gy, a 2-year actuarial complete response rate of 40% was found compared with 7, 4 and 0% at doses of 46-55 Gy, 36-45 Gy and less than or equal to 35 Gy, respectively. The dose-response relationship for local control also influenced the survival rate, although a number of patients died from distant metastases even when local control was obtained. However, with regard to locoregional disease, the 2-year survival was 53% for patients with complete tumour regression but only 8% for patients without complete tumour regression.