Proton Beam Therapy for Localized Prostate Cancer: Results from a Prospective Quality-of-Life Trial

Purpose: To report prostate cancer outcomes, toxicity, and quality of life (QOL) in men treated with proton beam therapy (PBT).

Patients and methods: Patients were enrolled in a prospective trial. All participants received 75.6 to 78 Gy (RBE). Up to 6 months of luteinizing hormone-releasing hormone agonist therapy was allowed. The Phoenix definition defined biochemical failure. Modified Radiation Therapy Oncology Group criteria defined toxicity. Expanded Prostate Cancer Index Composite questionnaires objectified QOL. Clinically significant QOL decrement was defined as ≥0.5 × baseline standard deviation.

Results: In total, 423 men were analyzed. The National Comprehensive Cancer Network risk classification was used (low 43%; intermediate 56%; high 1%). At the 5.2-year median follow-up, overall and disease-specific survival rates were 99.8% and 100%, respectively. Cumulative biochemical failure rate was 5.2% (95% confidence interval [CI] = 3.0%-8.3%); acute grade 2 genitourinary (GU) toxicity was 46.3%; acute grade 2 gastrointestinal (GI) toxicity was 5.0% (95% CI = 3.1%-7.3%). There was no acute grade ≥3 GI or GU toxicity. Cumulative late grade 2 GU and GI toxicity was 15.9% (95% CI = 13%-20%) and 9.7% (95% CI = 6.5%-12%), respectively. There were 2 grade 3 late GI toxicities (rectal bleeding) and no late grade ≥3 GU toxicity. The 4-year mean Expanded Prostate Cancer Index Composite urinary, bowel, sexual, and hormonal summary scores (range; standard deviation) were 89.7 (43.8-100; 11), 91.3 (41.1-94.6; 10), 57.8 (0.0-96.2; 27.1), and 92.2 (25-95.5; 10.5), respectively. Compared with baseline, there was no clinically significant decrement in urinary, sexual, or hormonal QOL after treatment completion. A modest (<10 points), yet clinically significant, decrement in bowel QOL was appreciated throughout follow-up.

Conclusion: Contemporary PBT resulted in excellent biochemical control, minimal risk of higher-grade toxicity, and modest QOL decrement. Further investigation comparing PBT with alternative prostate cancer treatment strategies are warranted.