ESTRO 2024 - Abstract Book

S417

Brachytherapy - Urology

ESTRO 2024

1 CHU de Québec – Université Laval, Radiation oncology, Quebec, Canada. 2 CRCHU de Québec and Centre de recherche sur le cancer de l’Université Laval, centre de recherche, Quebec, Canada. 3 Université-Laval, Département de physique, de génie physique et d’optique, Quebec, Canada

Purpose/Objective:

To evaluate efficacy, safety and biochemical cure of ultra hypo-fractionated (UHF) radiotherapy combined with high dose rate (HDR) brachytherapy boost (BB) in comparison to a moderately hypo-fractionated (MHF) regimen, in patients treated for intermediate risk prostate cancer according to National Comprehensive Cancer Network (NCCN) guidelines.

Material/Methods:

In this prospective single institution study, 201 patients with intermediate risk prostate cancer were recruited to the experimental treatment of 25 Gy in five fractions (Hypo 5 trial NCT05786742) using image-guided radiotherapy (IGRT) plus a 15 Gy HDR BB. They were compared to two historical control groups, treated with either 36 Gy in 12 fractions or 37.5 Gy in 15 fractions with an identical HDR BB. The control groups included 152 and 314 patients respectively. Follow up visits and PSA testing were scheduled six weeks after the implant and every 4 months for the first year, then every 6 months for years 2 to 5 and yearly thereafter. The biochemical cure after brachytherapy (PSA <0.2ng/ml) > 4 years was defined according to the criteria defined by Crook et al [1], based on biochemical failure after radical prostatectomy. Biochemical relapse free survival (BRFS) according to the Phoenix definition (PSA> nadir+2ng/ml), overall survival (OS), genitourinary (GU), international prostate symptom score (IPSS) and gastro intestinal (GI) and sexual toxicities sexual health inventory for men (SHIM) were also reported. Difference between groups were analyzed using Pearson chi square test for statistical analysis. At the time of analysis, median follow up was 24 months for the 25 Gy group, 76 months for the 36 Gy group and 88 months for the 37.5 Gy group. Median age was similar between groups. ISUP 1 and 2 disease rate were respectively 2%, 78.6% in 25/5 group, 0% and 67.1% in 36/12 group and 0.6% and 6.6% in 37.5/15 group. ISUP 3 disease was less important in 25/5 (19.4%) compared to 36/12 (32.9%), 37.5/15(32.8%) (p=0.003). Use of ADT was less frequent in the 25/5 (23.55%) and 37.5/15 (34.4%) groups compared to 36/12 (48.7%) group (p<0.001). The biochemical cure rate (BCR) was 72.2%, 78.8% and 69.4% of patients in the UHF and both MHF groups, respectively (p = 0.11). Estimated BRFS at 60 months was 97.5% for the UHF group, 96.6% for the 36 Gy arm and 96.3% for the 37.5 Gy arm (p=0.678 and p=0.188). There was no statistical difference in OS between the three groups at 60 months. Acute grade 2 GU toxicities were significantly lower in the UHF group (77.35%) compared to the other groups (85.5% and 82.5%) (p<0.001). There was no grade 3 in 25/5 group compared to 0.7% in 36/6 and 5.1% in 37.5/15. The acute IPS scores were also lower in the 25/5 group (7) compared to 36/12 (9) and 37.5/15 (11) (p<0.01). IPSS pre treatment, number of fractions (5 or 12), use of ADT are all significantly associated with better acute IPSS (p=0.001). The use of UHF was associated with significantly less Grade 1 GI toxicities with respective values of 17,2%, 19,7%, and 6,6% for the 36/12, 37,5/15 and 25/5 groups (p=0.002). Grade 2 toxicities were low 1,3%, 1,3%, and 1% respectively. The absence of ADT was also associated with better early GI toxicities (p=0.001). Acute SHIM was statistically different between 25/5 group (6) and 36/12(4) and 37.5/15(3) (p<0.001). Age (67.9) and fractions (5 or 12) and absence of ADT were correlated with better early SHIM (p=0.004). No difference was found in late GU, GI and SHIM toxicities between groups. Results: