ESTRO 2024 - Abstract Book

S2339

Clinical - Urology

ESTRO 2024

1 Radiotherapiegroep, Radiotherapy, Deventer, Netherlands.

2 Radiotherapiegroep, Radiotherapy, Arnhem,

Netherlands

Purpose/Objective:

A brachytherapy boost for intermediate to high-risk prostate cancer increases biochemical disease-free survival, potentially improving overall survival, albeit at the risk of increased toxicity (1-4). We performed a prospective evaluation of tumour control, survival, toxicity and quality of life in a large modern cohort of intermediate to high risk prostate cancer patients treated with a high-dose-rate (HDR) brachytherapy boost after hypo-fractionated external beam radiotherapy (EBRT). The secondary aim was to find predictors for tumour control and survival aiding in patient selection and follow-up individualisation.

Material/Methods:

Patients with intermediate to high-risk prostate cancer according to the D'Amico classification, treated from February 2010 through August 2020, were prospectively followed. Treatment consisted of EBRT (Tomotherapy and VMAT: 58 Gy in 20 fractions to prostate and seminal vesicles or 62.5 Gy in 25 fractions with 50 Gy in 25 fractions elective pelvic lymph node irradiation), followed by a single fraction HDR-brachytherapy boost of 10 Gy to the prostate. Radiotherapy was combined with androgen deprivation therapy (ADT) up to two years. Data on biochemical disease-free survival (bDFS), overall survival (OS), toxicity and quality of life (QoL) were registered 3 monthly during the first year, and twice yearly to yearly thereafter up to ten years. Biochemical recurrence was defined according to the Phoenix-definition (PSA nadir + 2 ng/ml). Toxicity was scored according to CTCAE v3.0. QoL was measured using IPSS for urinary function, and for erectile and bowel complaints a Likert scale was used ranging from no to severe bother. Survival analysis of bDFS and OS was performed using the Kaplan-Meier method and uni- and multivariable Cox-regression. Additionally, competing risk analysis according to Fine and Gray was used for bDFS, taking mortality into account as a competing risk. No imputation for missing data was performed, since data was complete except for one missing Gleason score (0.3%). All data were analysed using R-studio version 4.3.0. P values≤0.05 indicated statistical significance. A total of 274 patients were analysed. Mean age was 69 years (standard deviation 5.6 years), with a median PSA pre treatment of 11.7 ng/ml (interquartile range [IQR] 8-20). Gleason score was 6 in 35 patients (12.8%), Gleason 7 in 123 (44.9%) and Gleason 8-10 in 115 (42%). MRI T-stage was T1b-T2b in 60 (21.9%), T2c in 28 (10.2%) and T3a-T4 in 186 (67.9%, one case T4). This resulted in 267 (97.4%) high and 7 (2.6%) intermediate risk patients. Twelve (4.4%) patients did not receive ADT, 118 (43,1%) underwent three months neo-adjuvant treatment and 144 (52.6%) received a combination of neo-adjuvant and adjuvant therapies. Median follow-up was 95 months (IQR 66-120). bDFS at 5 years was 84% (95% confidence interval [CI] 79-89%) and 76% (95%-CI 70-83%) at 8 years, and OS 92% (95%-CI 89-96%) and 76% (95%-CI 71-82%), respectively. For biochemical failure, a PSA nadir >0.1 ng/ml after treatment was the strongest predictor in uni- and multivariable analysis: univariable hazard ratio (HR) 9.2 (95%-CI 5.2-16.3, p<0.0001) and multivariable corrected for PSA, T-stage, Gleason score, age, ADT and number of EBRT fractions, a comparable HR of 11.9 (95%-CI 6.4-22.0, p<0.0001). Patients with an unmeasurable PSA nadir (<0.1 ng/ml) (n=209) had bDFS at 8 years of 88% (95%-CI 83-94) versus 31% (18-54%) with a nadir >0.1 ng/ml (p<0.0001) (Figure 1). Competing risk analysis showed similar results. PSA nadir >0.1ng/ml was also the most significant predictor for mortality: univariable HR 1.9 (95%-CI 1.2-3.1, p=0.009) and multivariable 2.0 (95%-CI 1.2-3.3, p=0.01). A 15% survival advantage was seen in patients at 8 years with a PSA nadir <0.1 ng/ml (from 65% to 80%) (Figure 1). A Results: