Assessing the impact of an alternative biochemical failure definition on radiation dose response for high-risk prostate cancer treated with external beam radiotherapy

This analysis using the CN + 2 failure definition continues to show a dose response for the high-risk group of patients. However, the dose-response characteristics differ from those estimated using the ASTRO definition. We observed that the position (TCD50) and steepness (γ50) of the dose-response curve changed with time as long as the TCP continued to decrease. This suggests that the dose response characteristics derived from data with longer follow-up may be different from those derived with shorter follow-up using the CN + 2 or similar failure definitions which do not back-date the failure. These changes in dose-response characteristics as well as the time dependence of dose response should be noted when investigators design dose escalation trials for the high-risk prostate cancer patients.