Patterns of care studies: dose-response observations for local control of adenocarcinoma of the prostate.

Five hundred seventy-four patients with prostate cancer treated by external beam radiation therapy in the United States in 1973 to 1975 have been analyzed comparing radiation dose with in-field recurrence. Dose-response effects are observed for all cases (p = less than .05) and T-2 and T-3 tumors, but not for T-0, T-1 and T-4 tumors. For doses calculated at the center of the prostate, these observations suggest optimal control is obtained at no more than 6000 rad for T-0 and T-1 tumors; 6000-6500 rad for T-2 tumors; 6500-7000 rad for T-3 tumors; and that greater than 7000 rad is required only for T-4 tumors. The paraprostatic dose calculated at a point 4 cm lateral to the center of the prostate also shows a correlation of dose with infield failure for all cases (p = .01). Observations in individual T states suggest optimal control is obtained at no more than 6000 rad for T-0, T-1 and T-2 tumors, 6500-6999 rad for T-3 and greater than or equal to 7000 rad for T-4. These data suggest that for T-2 and T-3 cancers, extension in the periprostatic region must be treated. A comparison of central dose vs. stage indicates institutional policy rather than cancer volume determines the radiation dose used in treating prostate cancer. A change in institutional policies to treat with optimal doses as indicated by this study would result in an overall increase in local control and a decrease in complications.