Top Line: What are the optimal dose constraints for the bowel when delivering ultrahypofractionated elective nodal irradiation for prostate cancer?
The Study: In the POP-RT trial, elective nodal irradiation improved disease free survival in patients with high risk prostate cancer. ENI for high risk disease is commonly employed when using standard fractionation and even moderate hypofractionation, but less so with SBRT where 5-fraction ENI has been associated with modest increase in GI toxicity. In this secondary analysis of two prospective trials, a bowel bag structure and individual bowel loops were retrospectively drawn for 59 patients who received 25 Gy in 5 fractions to the pelvic lymph nodes as part of prostate SBRT for unfavorable intermediate risk and high risk disease. The rate of acute and late grade 2 GI toxicity was 12% and 20% with no grade 3 toxicity. There was no significant association between bowel bag or bowel loop dosimetry and acute or late toxicity risk. The median D0.1cc was 25.4 Gy for small bowel and 25.8 Gy for large bowel. Given the low observed toxicity in the study, the authors proposed bowel bag objectives of Dmax <27Gy (35Gy), V25 <80cc (100cc), V24 <150cc (200cc), and V20 <320cc (380cc).
TBL: In this study, bowel toxicity was relatively mild and not significantly associated with any particular bowel bag dosimetric parameters. | Ong, Int J Radiat Oncol Biol Phys 2025
The Study: In the POP-RT trial, elective nodal irradiation improved disease free survival in patients with high risk prostate cancer. ENI for high risk disease is commonly employed when using standard fractionation and even moderate hypofractionation, but less so with SBRT where 5-fraction ENI has been associated with modest increase in GI toxicity. In this secondary analysis of two prospective trials, a bowel bag structure and individual bowel loops were retrospectively drawn for 59 patients who received 25 Gy in 5 fractions to the pelvic lymph nodes as part of prostate SBRT for unfavorable intermediate risk and high risk disease. The rate of acute and late grade 2 GI toxicity was 12% and 20% with no grade 3 toxicity. There was no significant association between bowel bag or bowel loop dosimetry and acute or late toxicity risk. The median D0.1cc was 25.4 Gy for small bowel and 25.8 Gy for large bowel. Given the low observed toxicity in the study, the authors proposed bowel bag objectives of Dmax <27Gy (35Gy), V25 <80cc (100cc), V24 <150cc (200cc), and V20 <320cc (380cc).
TBL: In this study, bowel toxicity was relatively mild and not significantly associated with any particular bowel bag dosimetric parameters. | Ong, Int J Radiat Oncol Biol Phys 2025