Session Item

To assess the impact of HDR brachytherapy boost (HDR-BT) against exclusive external beam radiotherapy (EBRT) in biochemical free survival (BFS) and metastatic free survival (MFS) in high-risk prostate cancer patients. We also analyse differences in the HDR-BT impact in MFS between high-risk patients and very-high-risk patients.

We performed a retrospective analysis of patients diagnosed with high and very-high risk prostate cancer. One group received exclusive EBRT including pelvis with a prostate dose of 77,4-78 Gy while another group received 46-54 Gy followed by a HDR-BT in 2 fractions of 7.5Gy or single fraction of 15 Gy. External radiotherapy in both groups was delivered with IMRT in 82% of patients. Androgen deprivation therapy was administered during 2.5 years. Survival rates and multivariate analysis were performed using Kaplan Meier and Cox regression models with SPSS v25. Toxicity was analyzed with CTCAE version 5.0 criteria.

With a mean age of 69.8 years and a median follow up of 64 months, 801 patients treated in our department from 2008-2020 were included in the analysis, 481 patients (60.05%) in the EBRT group and 320 (39.95%) in the HDR-BT group. 5-year BFS was 96.4% in HDR-BT group and 89.2% in EBRT group (p 0.004). The 5-year MFS was 96.9% in HDR-BT group and 92.4% in EBRT group (p 0.04) (image1).  We performed a multivariate analysis in order to adjust BFS and MFS in both treatment groups by age, histology, PSA level and T stage (image 2); we found for the HDR-BT group had a hazard ratio (HR) of  0.34 (CI95% 0.18-0.66; p 0.002) in BFS and a HR of 0.41 (CI95% 0.18-0.9; p 0,02) in MFS. The impact of HDR-BT in MFS was predominant in very-high-risk (log rank p 0.02) versus high-risk patients (log rank p 0.9), although the number of events was only 11 in high-risk and 31 in very-high-risk. Genitourinary toxicity: acute grade 2 or more was 1.73% and 3.22% in HDR-BT and EBRT group, whereas chronic toxicity was 3.34% and 3.11% respectively. Gastrointestinal toxicity: acute grade 2 or more was 3.22% and 2.07% in HDR-BT and EBRT group, whereas chronic toxicity was 1.27% and 3.45% respectively.

We found a benefit in metastatic survival in the HDR-BT boost group with a very acceptable grade of toxicity. HDT-BT should be considered standard of care in treatment for both high-risk and very-high risk prostate cancer patients. Although the HDR-BT impact in MFS was higher in very-high-risk patients, the differences were probably caused by the need for longer follow-up in high-risk patients.