Late Rectal Toxicity from Image-guided Intensity Modulated Radiotherapy for Prostate Cancer

Late rectal toxicity (LRT) was retrospectively evaluated in men with prostate cancer treated with image-guided intensity modulated radiotherapy (IG-IMRT).Between May 2008 and December 2009, 47 men with prostate adenocarcinoma were treated with IG-IMRT using in-room computed tomography (CT).The median time to grade 2 LRT was 12 months (range=1-24 months). Two of 3 men who developed grade 2 LRT had received treatment for diabetes, and the other was receiving anticoagulant/antiplatelet therapy (AC therapy). Their rectal wall V70 (the volume of rectal wall receiving 70 Gy) values were 12.6%, 13.0%, and 13.3%. Univariate analysis revealed that V70 of the rectal wall was the only significant risk factor for LRT (p=0.0073).No man with V70 ≤12.0% experienced grade 2 LRT. Strict rectal wall V70 ≤12% dose constraints should be considered when treating prostate cancer patients who are also receiving diabetic or AC therapy.