Toxicity Analysis of Dose Escalation From 75.6 Gy to 81.0 Gy in Prostate Cancer

Abstract

Several randomized trials have demonstrated a biochemical control advantage to an increase from the "conventional" 66 to 70 Gy range to the "high-dose" 75 to 81 Gy range; these trials have also, however, demonstrated a toxicity disadvantage. Our objective was to perform a toxicity analysis of a minor dose escalation (from 75.6 to 81.0 Gy) within this "high-dose" range. A total of 189 patients comprised the study population-119 received 75.6 Gy and 70 received 81.0 Gy. Acute, late, and final (at most recent follow-up) gastrointestinal (GI) and genitourinary (GU) toxicity were charted for each group and compared using the χ test. Ordered logit regression analyses were performed on each toxicity end point, using all major demographic, disease, and treatment factors as covariates. The 81.0 Gy group had higher rates of grade 2 acute GU (P < 0.001), late GU (P = 0.001), and late GI (P = 0.082) toxicity, a lower rate of acute GI toxicity (P = 0.002) and no notable differences in final GU (P = 0.551) or final GI (P = 0.194) toxicity compared with the 75.6 Gy group. The ordered logit regression analyses showed that only age (P = 0.019) and radiotherapy dose (P = 0.016) correlated with acute GU toxicity and only radiotherapy dose (P = 0.018) correlated with late GU toxicity. Only intensity modulated radiotherapy use (P = 0.001) correlated with acute GI toxicity; no factors correlated with late GI toxicity or final GU or GI toxicity. Although some increases in acute and late toxicity rates were observed with even a minor dose escalation from 75.6 to 81.0 Gy, notably no increases in final late GI or GU toxicity rates were observed.