Session Item

Propensity score-matching (PSM) based long-term outcome and toxicity comparison of EBRT versus EBRT plus HDR brachytherapy boost (HDR-BT boost).

744 prostate cancer patients were treated with either EBRT alone (n = 406) or EBRT plus HDR-BT boost (n=338) between 2002 and 2019 and were retrospectively compared in this monocentric study.  PSM was performed including age, Gleason score, initial PSA value, tumor stage, use of ADT, and risk group according to D´Amico. After PSM, 258 patient pairs (n = 516) were included into the final analysis. For EBRT alone, 33 fractions were applied using VMAT with a simultaneous integrated boost of 60 Gy (D₉₅) / 76.23 Gy (D_mean). For combined EBRT and HDR brachytherapy, EBRT was delivered in 46 Gy (D_Mean) in conventional fractionation, followed by two fractions HDR-BT boost with 9 Gy (D_90%) two and four weeks after EBRT. Genitourinary (GU) and gastrointestinal (GI) toxicity was evaluated utilizing the Common Toxicity Criteria for Adverse Events (version 5.0) and biochemical failure was defined according to the Phoenix definition. Toxicities were calculated for the total group without PSM. For all statistical analyses, R software environment for statistical computing and graphics (version 4.1; The R Foundation for Statistical Computing, Vienna, Austria) was used. All tests were two-sided with a level of significance set at p < 0.05.

The median follow-up was 95.3 months (range 0.5-230.7 months) in the propensity score-matched cohort (n = 516). 36 / 190 / 290 patients had low- / intermediate- / high-risk prostate cancer, respectively. Additive androgen deprivation therapy was given in 52.7% of the patients. Biochemical relapse-free survival (bRFS), metastasis-free survival (MFS), and overall survival (OS) for both groups were not statistically different after PSM. The estimated 10-year bRFS was 82.0% versus 76.3% (p = 0.075) for EBRT versus EBRT + HDR brachytherapy, respectively. The estimated 10-year MFS was 82.9% versus 87.4% (p = 0.19) and the 10-year OS was 65.7% versus 68.9% (p = 0.30). EBRT, compared to EBRT + HDR-BT boost, showed significantly higher acute toxicities and higher cumulative 5-year late GI toxicity ≥ grade 2: Acute GU toxicity ≥ grade 2 occurred in 25.9% vs 11.8% (p < 0.001) and acute GI toxicity ≥ grade 2 in 11.8% vs 2.7% (p < 0.001). Cumulative 5‑year late GU ≥ grade 2 toxicities were observed in 23.6% vs 19.2% (p = 0.086) and 5‑year late GI ≥ grade 2 toxicities in 11.1% vs 5.0% of the patients (p = 0.002). Cumulative 5‑year late grade 3 GU toxicity occurred in 4.2% and 3.6% (p=0.401) and GI toxicity in 1.0% and 0.3% (p=0.249) in both groups.

EBRT alone and combined EBRT + HDR-BT boost showed no differences in long-term biochemical relapse-free survival, metastasis-free survival, and overall survival. Acute toxicities and late gastrointestinal toxicity ≥ grade 2 were lower for the combined treatment.