Background: To assess genitourinary (GU) function and toxicity in patients treated with image-guided proton therapy (PT) for early- and intermediate-risk prostate cancer and to analyze the impact of pretreatment urinary obstructive symptoms on urinary function after PT.
Material and methods: Two prospective trials accrued 171 prostate cancer patients from August 2006 to September 2007. Low-risk patients received 78 cobalt gray equivalent (CGE) in 39 fractions and intermediate-risk patients received 78-82 CGE. Median follow-up was five years. The International Prostate Symptom Score (IPSS) and GU toxicities (per CTCAE v3.0 and v4.0) were documented prospectively.
Results: Five transient GU events were scored Gr 3 per CTCAE v4.0, for a cumulative late GU toxicity rate of 2.9% at five years. There were no Gr 4 or 5 events. On multivariate analysis (MVA), the only factor predictive of Gr 2 + GU toxicity was pretreatment GU symptom management (p = 0.0058). Patients with pretreatment IPSS of 15-25 had a decline (clinical improvement) in median IPSS from 18 before treatment to 10 at their 60-month follow-up. At last follow-up, 18 (54.5%) patients had a > 5-point decline, 14 (42.5%) remained stable, and two patients (3%) had a > 5-point rise (deterioration) in IPSS. Patients with IPSS < 15 had a stable median IPSS of 6 before treatment and at 60 months.
Conclusion: Urologic toxicity at five years with image-guided PT has been uncommon and transient. Patients with pretreatment IPSS of < 15 had stable urinary function five years after PT, but patients with 15-25 showed substantial improvement (decline) in median IPSS, a finding not explained by initiation or dose adjustment of alpha blockers. This suggests that PT provides a minimally toxic and effective treatment for low and intermediate prostate cancer patients, including those with significant pretreatment GU dysfunction (IPSS 15-25).