3295 - Evaluating Factors Related to Clinical Failure and Toxicity in Patients with Prostate Cancer Treated By a Low-Dose-Rate Brachytherapy

12:45pm - 02:00pm PT

Hall F

Screen: 18

POSTER

Presenter(s)

Yasushi Nakai, MD, PhD - Nara Medical University, Kashihara, Nara

Y. Nakai¹, N. Tanaka II¹, K. Onishi¹, Y. Kaori², I. Asakawa², and K. Fujimoto¹; ¹Department of Urology, Nara Medical University, Kashihara, Japan, ²Department of Radiation Oncology, Nara Medical University, Kashihara, Japan

Purpose/Objective(s):

This study evaluated factors associated with clinical failure and toxicity in patients with low-, intermediate-, and high-risk prostate cancer treated with low-dose-rate brachytherapy (LDR-BT) alone or combined with external beam radiation therapy (EBRT).

Materials/Methods:

Seven hundred thirteen patients (low risk: n = 323; intermediate-risk: n = 390) underwent LDR-BT alone, while 534 patients (intermediate-risk: n = 225; high risk: n = 309) underwent LDR-BT combined with EBRT. The Fine-Gray hazard model was used to identify factors associated with clinical failure. Clinical failure was defined as local recurrence, regional/distant metastasis, or biochemical triggers requiring salvage treatment. Youden index was employed to determine BED cut-off values for Grade 3 or higher toxicity.

Results:

In patients treated with LDR-BT alone, BED thresholds of =180 Gy2 (low-risk; hazard ratio [HR]: 0.38; 95% confidence interval [95% CI], 0.15–0.98, intermediate-risk; HR: 0.29; 95% CI, 0.12–0.70) was significantly associated with better clinical outcomes. Patients with Grade 3 or higher toxicity had significantly higher BEDs than those without toxicity (p = 0.008). A BED threshold of 200 Gy2 was identified as a cut-off value for toxicity risk.

In patients treated with LDR-BT combined with EBRT, BED was not significantly associated with improved clinical failure-free rates. Neoadjuvant androgen deprivation therapy was significantly associated with improved better clinical outcomes in patients with intermediate-risk prostate cancer treated with LDR-BT combined with EBRT (HR: 0.13; 95% CI, 0.03–0.57). A primary Gleason Grade 5 was significantly associated with worse clinical outcomes in patients wtih high-risk prostate cancer treated with LDR-BT combined with EBRT (HR: 3.03; 95% CI, 1.22–7.55). Patients experiencing Grade 3 or higher toxicity exhibited significantly higher BEDs than those without toxicity (p = 0.04). A BED cut-off of 220 Gy2 was determined for toxicity.

Conclusion:

For patients undergoing LDR-BT alone, a BED of 180–200 Gy2 appears optimal. For those undergoing LDR-BT combined with EBRT, a BED of 200–220 Gy2 may be more appropriate.