3392 - Combination Low-Dose-Rate Brachytherapy and Stereotactic Body Radiation Therapy (SBRT) In Localized Intermediate- and High-Risk Prostate Cancer: A Single Institution Experience

Title: Combination Low-Dose-Rate Brachytherapy and Stereotactic Body Radiation Therapy (SBRT) in Localized Intermediate- and High-Risk Prostate Cancer: A Single Institution Experience

Purpose/Objective(s):

Findings from multiple large, randomized trials suggest that radiation therapy dose escalation in prostate cancer results in improved biochemical control. Combination low-dose-rate brachytherapy and SBRT may be a safe and effective method to dose-escalate therapy in patients with localized NCCN intermediate- and high-risk prostate cancer. We report on our single institution experience utilizing this treatment modality.

Materials/Methods:

We reviewed the charts of 137 prostate cancer patients treated with combination low-dose-rate (Pd-103) brachytherapy (prescription dose, 100 Gy) prostate seed implant and SBRT (25 Gy in 5 fractions) to the prostate and seminal vesicles from 2018 to 2025. Patients received brachytherapy followed by SBRT approximately one month later. The International Prostate Scoring System (IPSS) and Sexual Health Inventory for Men (SHIM) were used to capture patient reported quality-of-life metrics at baseline and at follow-ups.

Results:

The mean age of the cohort was 68 years with median pre-treatment baseline PSA of 7.6 ng/mL. The median follow-up was 42 months. Per NCCN Risk Group Classification, most patients were unfavorable intermediate risk (91, 66%) and there were similar distributions between favorable intermediate (22,16%) and high-risk groups (24, 18%). Fourteen (10%) patients in total received short-course androgen deprivation therapy as part of their initial treatment course.

Overall survival at 5 years was 97.7% with three deaths unrelated to disease. Overall, there were eight patients with recurrent disease. Locoregional control was 94.5% at 5 years with four patients found to have PSMA PET avid pelvic lymph node recurrence and one patient with biopsy-proven prostate local recurrence 3.5 years post-treatment. Distant failure free survival at 5 years was 94% with three patients developing osseous metastasis identified on PSMA PET.

The biochemical recurrence free survival at 5 years was 84% where biochemical failure was defined as PSA nadir + 0.4 ng/mL. Using this criteria, ten patients developed biochemical failure. Six of these patients were found to have recurrent disease as discussed previously, two had subsequent decrease in PSA, and two are pending repeat PSA.

The median baseline IPSS of patients with mild or moderate urinary symptoms (IPSS < 20) was 5; the mean baseline SHIM of potent patients (SHIM > 20) was 23. Post-treatment median IPSS at 3, 12, and 24 months were 14 (IQR 9 to 18), 12 (9 to 17), and 8 (5.5 to 16) respectively. Post-treatment median SHIM at 6 and 12 months were 17 (8 to 21) and 17.5 (11 to 21) respectively. There was no CTCAE v5 grade 2+ rectal bleeding.

Conclusion:

For localized intermediate and high-risk prostate cancer patients, combination low-dose-rate brachytherapy with SBRT is an effective and safe treatment modality.