Pelvic chemoradiation with high-dose-rate brachytherapy boost for synchronous prostate and rectal cancers: A rare...

Synchronous prostate and rectal cancers pose therapeutic challenges. Prostate external beam radiation therapy may increase rectal dose and impair anastomotic healing after chemoradiation (CRT). High-dose-rate brachytherapy (HDR-BT) enables prostate dose escalation, minimizing rectal exposure. We report outcomes of pelvic CRT plus HDR-BT boost and propose a treatment algorithm.

We retrospectively reviewed a multi-institutional database (2011-2023) to identify patients with synchronous prostate and rectal/anal cancers treated with curative intent. All received pelvic CRT (45-50.4 Gy/25-28 fractions) with concurrent 5-FU or capecitabine ± total neoadjuvant therapy. HDR-BT boosts were delivered to the prostate ± seminal vesicles, meeting objectives of prostate V100 ≥ 95%, rectum V75% < 1 cc, and urethra D10 ≤ 115%. Toxicities were graded per CTCAE v5.0; oncologic outcomes were assessed.

Six men (age 60-78) completed CRT, HDR-BT, and surgery/nonoperative management without interruptions. At median 40 months (range 30-110) follow-up post-BT, no locoregional failures occurred; two rectal cancers achieved pathologic complete response, and four remained recurrence-free. All prostate cancers were biochemically controlled; two rectal cancers developed distant metastasis at ∼2-3 years. HDR-BT achieved excellent prostate coverage (V100 94.6%-97.7%, D90 103%-108%) and rectal sparing (D2cc 40%-72% of prescription, V75 ≤ 1.4 cc). One late grade 3 proctitis/urethral stricture occurred in a fractionated high-dose case; none ≥ grade 3 GU/GI in the single-fraction cohort.

CRT followed by HDR-BT prostate boost is feasible, maintains anastomotic safety, and achieves excellent local control and dosimetry with minimal severe toxicity.