Acute toxicity and its dosimetric correlates for high-risk prostate cancer treated with moderately hypofractionated radiotherapy

Abstract Aims To report the acute toxicity and the dosimetric correlates after moderately hypofractionated radiotherapy for localized prostate cancer. Methods A total of 101 patients with localized prostate cancer were treated with image-guided intensity-modulated radiation therapy. Patients were treated to 65 Gy/25 Fr/5 weeks ( n = 18), or 60 Gy/20 Fr/4 weeks ( n = 83). Most (82.2%) had high-risk or pelvic node-positive disease. Acute toxicity was assessed using Radiation Therapy Oncology Group (RTOG) acute morbidity scoring criteria. Dose thresholds for acute rectal and bladder toxicity were identified. Results The incidence of acute grade 2 GI toxicity was 20.8%, and grade 2 genitourinary (GU) toxicity was 6.9%. No Grade 3 to 4 toxicity occurred. Small bowel toxicity was uncommon (Gr 2 = 4%). The 2 Gy equivalent doses (EQD2) to the rectum and bladder (α/β = 3) calculated showed that the absolute doses were more consistent predictors of acute toxicities than the relative volumes. Those with grade 2 or more GI symptoms had significantly higher V EQD2-60 Gy (13.2 vs 9.9 cc, p = 0.007) and V EQD2-50 Gy (20.6 vs 15.4 cc, p = 0.005). Those with grade 2 or more GU symptoms had significantly higher V EQD2-70 Gy (30.4 vs 18.4 cc, p = 0.001) and V EQD2-65 Gy (44.0 vs 28.8 cc, p = 0.001). The optimal cutoff value for predicting grade 2 acute proctitis, for V EQD2-60 Gy was 9.7 cc and for V EQD2-50 Gy was 15.9 cc. For grade 2 GU symptoms, the threshold values were 23.6 cc for V EQD2-70 Gy and 38.1 cc for V EQD2-65 Gy. Conclusions Hypofractionated radiotherapy for prostate cancer is well tolerated and associated with manageable acute side effects. The absolute dose-volume parameters of rectum and bladder predict for acute toxicities.