Ten-year outcomes for image-guided moderately hypofractionated proton therapy for prostate cancer.

PURPOSE: To report 10-year outcomes after image-guided moderately hypofractionated proton therapy for prostate cancer.

MATERIALS AND

METHODS

Using an IRB-approved, single institutional prospective outcomes registry at our institution between 2008 and 2015, we updated the previously reported outcomes results of 582 prostate cancer patients treated with double-scattered moderately hypofractionated proton therapy. Two hundred and seventy-one patients had low-risk, and 311 had intermediate-risk disease, including 148 with favorable intermediate-risk and 163 with unfavorable-intermediate-risk. The compressed course of proton therapy consisted of 70.0 GyRBE (2.5 GyRBE/fraction) for low-risk and 72.5 GyRBE for intermediate-risk patients. Seventeen patients received androgen deprivation therapy for a median six months.

RESULTS

Median follow-up was 10.2 years (range, 1.0-15.1). Freedom from disease progression overall and in low-risk and intermediate-risk subsets were 91.9%, 95.9%, and 88.4%, respectively. Favorable intermediate-risk and unfavorable-intermediate-risk subsets were 94.0% and 82.7%, respectively. Local recurrence occurred in 3.6% of patients. The cumulative incidences of 10-year grade 2 gastrointestinal, grade 3 gastrointestinal, and grade 3 genitourinary toxicities were 12.0%, 1.4%, and 2.7%, respectively. No grade ≥ 4 gastrointestinal or genitourinary toxicities occurred. The proportion of patients developing second malignancies is 7.2% overall, 4.6% with the exclusion of non-melanomatous skin cancers, 2.9% for cancers developing more than five years after proton therapy, and only 1.7% for in-field and/or pelvic cancers.

CONCLUSION

With a median follow-up over ten years, this report establishes the durability of excellent outcomes with moderately hypofractionated proton therapy including high efficacy, minimal physician-assessed toxicity, excellent patient-reported outcomes, and a low proportion of patients developing second malignancies. The excellent but slightly lower rate of disease control in intermediate risk patients may reflect the conservative use of androgen deprivation therapy during this time frame.