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

To report the acute toxicity and the dosimetric correlates after moderately hypofractionated radiotherapy for localized prostate cancer.

A total of 101 patients with localized prostate cancer were treated with image-guided intensity-modulated radiation therapy. Patients were treated to 65Gy/25Fr/5 weeks (n = 18), or 60Gy/20Fr/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.

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 2Gy 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_EQD2-60Gy (13.2 vs 9.9cc, p = 0.007) and V_EQD2-50Gy (20.6 vs 15.4cc, p = 0.005). Those with grade 2 or more GU symptoms had significantly higher V_EQD2-70Gy (30.4 vs 18.4cc, p = 0.001) and V_EQD2-65Gy (44.0 vs 28.8cc, p = 0.001). The optimal cutoff value for predicting grade 2 acute proctitis, for V_EQD2-60Gy was 9.7cc and for V_EQD2-50Gy was 15.9cc. For grade 2 GU symptoms, the threshold values were 23.6cc for V_EQD2-70Gy and 38.1cc for V_EQD2-65Gy.

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.