Combined Low Dose Rate Brachytherapy and External Beam Radiation Therapy for Intermediate-Risk Prostate Cancer

This is a retrospective study conducted to report the tumor control and late toxicity outcomes of patients with intermediate-risk prostate cancer undergoing combination external beam radiation therapy and low dose rate brachytherapy (LDR-PB).

Thirty-one patients received 45 Gray (Gy) of external beam radiation therapy to the prostate and seminal vesicles, together with a brachytherapy boost via a transperineal prostate implant of I¹²⁵ (108 Gy). In addition, some patients received 6 months of androgen deprivation therapy depending on physician preference. Biochemical failure was defined using the Phoenix consensus definition of the nadir PSA +2 ng/mL. Toxicity was graded using the Common Terminology Criteria for Adverse Events version 4.0.

The biochemical progression-free survival, metastases-free survival, and overall survival at 5 years were 87.1%, 96.3%, and 92%, respectively. The incidence of late grade ≥1 and ≥2 genitourinary (GU) toxicities were 54.8% and 6.5%, respectively. The incidence of late grade 3 GU toxicity was 6.5% with urinary retention occurring in two patients requiring either a bladder neck incision or transurethral resection of the prostate. The incidence of late grade ≥1 and 2 gastrointestinal toxicities were 19.4% and 6.5%, respectively. No patients developed grade 3 gastrointestinal toxicity.

Our small series has shown a high biochemical progression-free survival consistent with the ASCENDE-RT and NRG Oncology/RTOG0232 LDR-PB boost arms. In addition, the risk of late grade 3 GU toxicity is far lower than that reported by the ASCENDE-RT study but comparable to other LDR-PB boost and LDR alone reports in the literature. Therefore, we are comfortable to continue offering LDR-PB boost to our patients with intermediate-risk prostate cancer.