PPP05 Presentation Time: 11:06 AM

Purpose

Brachytherapy boost has been shown to improve biochemical control when added to external beam radiotherapy (EBRT) in patients with unfavorable intermediate- and high-risk prostate cancer. We report the safety and early efficacy of using proton therapy (PT) and low-dose-rate (LDR) brachytherapy boost at the University of Texas MD Anderson Cancer Center.

Methods and Materials

A retrospective study was conducted, including all patients with intermediate- or high-risk prostate cancer treated with a combination of PT and LDR boost with or without androgen deprivation therapy (ADT), from 2010 until 2023. Patient, initial disease, and treatment characteristics and toxicity and efficacy outcomes were collected. Biochemical failure (BF) was defined per the Phoenix definition (nadir PSA + 2).

Results

One hundred patients received PT and LDR boost, with median age at diagnosis of 68 (IQR 61-72). Most patients (n=78) were Caucasian, 12 were Black, 5 Asian, 3 Hispanic. Thirty-five patients had NCCN intermediate-risk (4 favorable and 31 unfavorable), 55 had high- and 10 had very high-risk disease. The median PT and LDR doses were 44 CGE (range 40-50.4) and 90 Gy (range 90-110). Pd-103 was used in 96 patients, I-125 in 4 patients, and 91 patients had MRI-assisted radiosurgery (MARS) brachytherapy. ADT was used in 92 patients. Rectal spacer was used in 22 patients. After a median follow-up of 43 months, two patients developed BF for a 5-year biochemical recurrence-free survival of 95%. Of the 2 patients with BF, one patient had a PSA 3.2 at 23 months and unknown disease site recurrence and the second developed lymph node metastasis when PSA was 5.1 at 60 months and is receiving intermittent ADT. No patients developed local recurrence or distant metastasis, and none died of prostate cancer. One patient died of other causes with PSA <0.1 at time of death. One patient has increasing PSA but has not met BF criteria. Median PSA nadir was 0.01 (range 0.0-0.4). All patients (n=30) with at least 4 years of PSA follow-up achieved a nadir PSA of 0.2 or less. Four patients had acute urinary retention. Late grade 2 GU or GI toxicity was found in 11 patients (11%) and 3 patients (3%), respectively. Only one patient had a grade 3 toxicity (urethral stricture requiring dilatation and TURP).

Conclusions

Acknowledging the intermediate follow-up duration, PT and LDR boost with and without ADT can achieve high control rates and low toxicity for prostate cancer patients with unfavorable intermediate and high-risk prostate cancer. MARS has enabled the use of MRI at each step of the quality assurance process.