Single institution, retrospective comparison of toxicity and outcome for static 5-field IMRT versus VMAT in the delivery of prostate and pelvic nodal irradiation in high-risk prostate cancer.

Abstract

147 Background: There is emerging evidence for the role of pelvic nodal irradiation in high-risk prostate cancer. We have assessed the toxicity rates and outcomes with 2 different radiotherapy techniques. Methods: The baseline disease metrics, toxicity and outcome data for men treated at our institution with prostate and pelvic nodal irradiation during a 2 year period were retrospectively collected. The radiotherapy technique, either 5-field IMRT or VMAT was recorded along with a single dose-level to indicate normal tissue exposure (V50 to bowel and rectum, that is the percentage of total organ receiving ≥ 50Gy). Results: 67 men with a median age of 64 years were identified; 83.6% were Gleason ≥ 8, 82.1% were ≥ T3a, 50.7% were N1, 4.5% were M1a/M1b. All had neoadjuvant and concurrent hormone therapy. All received 74Gy to prostate; 70.1% received 60Gy to pelvic nodes, 28.4% received 55Gy to pelvic nodes (1 patient received 56Gy). 55.2% were treated with static IMRT and 44.8% with VMAT with no significant difference in nodal dose received by static vs VMAT groups. Median follow up was 25 months. Analysis found V50 rectum was significantly lower in those treated with VMAT compared to static IMRT (48.5% vs 54.76% p = 0.001). Acute bowel toxicity rates (RTOG grade) were 80.6% grade < 2, 19.4% grade 2, nil > grade 2. Late bowel toxicity rates (RTOG grade) were 88% grade < 2, 12% grade 2, nil > grade 2. There was no significant difference in rates of acute or late bowel toxicity in groups treated with static IMRT vs VMAT. 13 patients (19.4%) underwent lower GI endoscopy during follow up, 9 had radiation proctitis. There was no significant difference in rates of endoscopy or proctitis for VMAT vs IMRT groups. 11.9% of patients developed biochemical failure during follow up. Rates of biochemical failure were not significantly different in groups separated by dose to pelvic nodes or radiotherapy technique. Conclusions: In a single institution, retrospective analysis, prostate and pelvic nodal irradiation is associated with acceptable rates of toxicity. Treatment with VMAT is associated with a significantly lower V50 rectum than that delivered by static IMRT.