Five-Year Biochemical Results, Toxicity, and Patient-Reported Quality of Life After Delivery of Dose-Escalated Image Guided Proton Therapy for Prostate Cancer

Abstract

Purpose: To report clinical outcomes in patients treated with image guided proton therapy (PT) for localized prostate cancer.

Methods and materials: The medical records of 1327 men were reviewed. Each man was enrolled on an outcomes tracking study. Dual enrollment on a prospective clinical trial was allowed. Each patient was treated for localized prostate cancer with PT at our institution between 2006 and 2010. Ninety-eight percent of patients received 78 Gy (radiobiological equivalent [RBE]) or higher; 18% received androgen deprivation therapy (ADT). The 5-year freedom from biochemical progression (FFBP), distant metastasis-free survival, and cause-specific survival rates are reported for each risk group. Data on patient-reported quality of life and high-grade toxicities were prospectively collected and reported. A multivariate analysis was performed to identify clinical predictors of biochemical failure and urologic toxicity.

Results: The median follow-up time was 5.5 years. The 5-year FFBP rates were 99%, 94%, and 74% in low-risk, intermediate-risk, and high-risk patients, respectively. The actuarial 5-year rates of late grade 3+ Common Terminology Criteria for Adverse Events, version 4.0, gastrointestinal (GI) and genitourinary (GU) toxicity were 0.6% and 2.9%, respectively. Multivariate analysis showed a significant correlation between grade 3+ GU toxicity and pretreatment prostate reductive procedures (P<.0001), prostate volume (P=.0085), pretreatment α-blockers (P=.0067), diabetes (P=.0195), and dose-volume histogram parameters (P=.0208). The median International Prostate Symptom Scores pretreatment scores and scores at 5 years after treatment were 7 and 7, respectively. The mean Expanded Prostate Cancer Index Composite (EPIC) scores significantly declined for sexual summary for patients not receiving ADT (from 67 to 53) between baseline and 5 years.

Conclusions: Image guided PT provided excellent biochemical control rates for patients with localized prostate cancer. The actuarial rates of high-grade toxicity were low after PT. From pretreatment to 5 years of follow-up, a significant decline was found only in mean EPIC sexual summary scores. Prospective clinical studies are needed to determine the comparative effectiveness of PT and other radiation treatment strategies.