Comparison of late rectal toxicity from conventional versus three-dimensional conformal radiotherapy for prostate cancer: Analysis of clinical and dosimetric factors

Abstract Objectives To compare late rectal toxicity (LRT) after definitive radiotherapy (DR) and salvage radiotherapy (SR) in prostate cancer using conventional (CONV) or three-dimensional conformal (3-D) techniques. Methods The outcomes and clinical factors of 212 patients with Stage T1a-T4 prostate cancer were evaluated (separated into DR and SR groups). The median prescribed dose was 66, 74, 66, and 70 Gy, for the CONV-DR, 3-D-DR, CONV-SR, and 3-D-SR groups, respectively. LRT was scored using both Radiation Therapy Oncology Group (RTOG) and modified RTOG and Late Effects Normal Tissue (mRTOG/LENT) scales. Results The 4-year biochemical relapse-free survival rate was 83% for all patients, with a trend toward improvement in the 3-D groups (78% CONV and 85% 3-D, P = 0.12). One patient (1%) in the CONV group and 24 (24%) in the 3-D group experienced grade 2 or worse LRT by the mRTOG/LENT scale. Patients undergoing DR experienced grade 2 or worse LRT of 1% versus 21% ( P = 0.003) for the CONV and 3-D groups, respectively. Patients undergoing SR experienced grade 2 or worse LRT of 0% versus 40% for the CONV and 3-D groups, respectively. The following variables correlated significantly with LRT on both univariate and multivariate analyses: prescribed radiation dose ( P P P P >0.05). Conclusions The prescribed radiation dose and percentage of rectal volume treated to 60 or 70 Gy had statistically significant correlations with increased LRT. The rate of grade 2 or worse LRT was greater for patients undergoing SR than for those undergoing DR. We believe that continued close attention to dosimetric variables is imperative for future studies of dose escalation.