Proton Therapy in the Management of Localized Prostate Cancer in Young Men

We present long-term outcomes of men young aged 50 years or younger treated for localized prostatic adenocarcinoma with image-guided proton therapy (PT).

We identified 85 patients with localized prostate cancer treated with PT between 2006 and 2017 at our institution. Patients were treated with double scattered PT to a median dose of 78 GyRBE (range, 78-82) delivered at 2 GyRBE/fraction. Nine (11%) received androgen deprivation therapy for a median of 6 months (range, 6-7). Biochemical control was defined by the Phoenix Definition. Physician-reported toxicity assessed according to CTCAE v5.0. Patient reported outcomes were assessed with the International Prostate Symptom Score and Expanded Prostate Index Composite (EPIC). Freedom from Biochemical Failure (FFBF) was tabulated with Kaplan-Meier method.

Median follow-up was 12.3 years (range, 1.58-17.4). FFBF rates by risk category at 10 years were very low 100%, low 100%, favorable intermediate 92%, unfavorable intermediate 93%, and high 100%. Three developed disease progression at 10 years. All had biochemical progression, and one recurred with regional nodal metastases. Grade 2+ gastrointestinal toxicity occurred in 2 (2.4%), and grade 3+ urologic toxicity occurred in 2 (2.4%). Median EPIC summary scores for urinary and bowel outcomes were 97.1 and 98.1 at baseline and 95.8 and 96.4 at 10 years respectively. Median EPIC sexual summary score was 82.7 at baseline and 69.2 at 10 years respectively. Two patients developed a second cancer, and both were out-of-field. One occurred in the submandibular gland 7 years after treatment, and the other in the pancreas 10 years after treatment.

PT provides excellent tumor control for patients 50 years or younger with localized prostate cancer and has a low risk for high-grade toxicities. No in-field secondary cancers were observed. Findings from this relatively small population should be confirmed in a larger study population.