ESTRO 2024 - Abstract Book

S413

Brachytherapy - Urology

ESTRO 2024

Brandon Morales 1,2,3 , Damien Carignan 1,3 , Philippe Després 1,4,5 , William Foster 1,2 , André-Guy Martin 1,2,3 , Eric Vigneault 1,2,3 1 Centre de Recherche du CHU de Québec-Université Laval, Axe Oncologie, Québec, Canada. 2 CHU de Québec Université Laval, Service de Radio-Oncologie, Québec, Canada. 3 Centre de Recherche sur le Cancer de l’Université Laval, Faculté de Médecine, Québec, Canada. 4 Faculté des Sciences et de Génie de l’Université Laval, Département de Physique, Génie Physique et Optique, Québec, Canada. 5 Centre de Recherche de l’Institut Université de Cardiologie Pneumologie de Québec, Département de Physique, Québec, Canada

Purpose/Objective:

Prostate cancer (PCa) remains a leading cause of morbidity and mortality among men worldwide. Its accurate risk stratification is paramount to guide treatment decisions and improve outcomes given today's therapeutic arsenal, particularly for higher-risk PCa patients. Numerous risk stratification tools have been developed to this effect. However, many of these tools were designed to predict surrogate endpoints and their validation in patients treated with HDR brachytherapy remains unexplored. We report the outcomes of high-risk PCa, initially classified according to the 3-tier NCCN classification system and treated with external beam radiation therapy (EBRT), high dose-rate brachytherapy boost (HDR-BT), and androgen deprivation therapy (ADT). Our study aims to provide external validation of the CAPRA score and the 5-tier NCCN classification system as pretreatment risk stratification tools to predict the risk of metastasis and death in this population.

Material/Methods:

We included 469 high-risk PCa patients according to the 3-tier NCCN classification. Individuals were treated with EBRT, HDR-BT, and ADT between 1999 and 2018 at our institution. Their clinical characteristics, treatments received, and outcomes were retrospectively analyzed. We conducted competing-risk survival analyses to compare individuals with CAPRA scores <6 versus ≥6 for biochemical relapse (BCR) and metastasis incidence. We also assessed both groups' overall survival (OS) using Kaplan-Meier analysis. The same analyses were repeated for the 5 tier NCCN stratification, comparing those classified as high versus very-high risk. Finally, we used ROC curve analyses to evaluate the predictive abilities of both stratification systems.

Results:

Patients' median age at time of implant was 71 years. The median follow-up period was 72 months (IQR 55-105). Assuming an α/β ratio of 1.93 for prostate cancer, our cohort received an EQD2 of 74 Gy or greater, with a median EQD2 of 107 Gy (IQR 98-110 Gy). The median prescribed duration of ADT was 24 months (IQR 12-36 months). Both a CAPRA score ≥6 and belonging to the NCCN very high -risk group were associated with BCR, with sHRs of 3.16 (p=0.011) and 2.27 (p=0.023), respectively. The CAPRA score yielded a sHR of 2.87 for metastasis incidence, whereas the NCCN showed a sHR of 2.22, almost reaching significance in both instances (p=0.06, and p=0.07, respectively). For 10- year OS, having a CAPRA score ≥6 and belonging to the NCCN very -high-risk group had similar HRs of 1.92 (p=0.015) and 1.88 (p=0.0082) for mortality. The ROC analysis revealed consistent AUC values around 0.6 for both tools, not reaching statistical significance in either case.

Conclusion: