ESTRO 2024 - Abstract Book

S2344

Clinical - Urology

ESTRO 2024

Michael Cardoso 1 , Matthew Richardson 2 , Phillip Chlap 1 , Sarah Keats 1 , Alan Glyde 3 , Sankar Arumugam 1 , David Pryor 3 , Joseph Bucci 4 , Jarad Martin 2 , Mark Sidhom 1 1 Liverpool and Macarthur Cancer Therapy Centres, Radiation Oncology, Liverpool, Australia. 2 Calvary Mater, Radiation Oncology, Newcastle, Australia. 3 Princess Alexandra Hospital, Radiation Oncology, Brisbane, Australia. 4 St George Hospital, Cancer Care Centre, Radiation Oncology, Kogarah, Australia

Purpose/Objective:

Delayed genitourinary toxicity is reported following definitive stereotactic radiotherapy for prostate cancer in up to 14.5% of patients 1 . The purpose of this study is to investigate whether there is a relationship between radiation dose to the bladder or urethra to genitourinary toxicity grade > 2 (CTCAE 4.0) in patients treated with stereotactic radiotherapy.

Material/Methods:

PROMETHEUS is a phase 2 multicenter trial exploring a stereotactic radiotherapy boost to the prostate combined with fractionated external beam radiotherapy as a virtual high dose rate brachytherapy (VHDR) boost in intermediate and high risk prostate cancer patients 2 . Instead of dose escalation using a high-dose-rate brachytherapy boost, the PROMETHEUS trial explores delivering comparable radiotherapy doses with stereotactic radiotherapy techniques, giving 20Gy in 2 fractions delivered one week apart, followed by 46Gy in 23 fractions of conventional external beam radiotherapy. Radiotherapy plans were reviewed to examine organs at risk including the bladder and the urethral planning target at risk volume (PRV) and this was correlated with patient reported genitourinary toxicity occurring 6 months or greater following stereotactic radiotherapy. Metrics used included prostate volume, urethral PRV volume, urethral mean dose, bladder D0.1cc, D10cc, D15cc, V8, V9, V10, V12, V14, V16, V17 and V19. Univariant and multivariant analysis were conducted to compare metrics for patients with and without genitourinary toxicity. A total of 87 patients from five centers were assessed and 19.5% of these patients experienced grade >2 genitourinary radiotherapy related toxicity, more than 6 months after stereotactic radiotherapy. Prostate volume did not predict for genitourinary toxicity. On univariant analysis, the urethral PRV volume, bladder D10cc, bladder D15cc and bladder V8 were predictive of genitourinary toxicity with a p value of less than 0.05. The mean with a 95% confidence interval was established. The mean urethral PRV volume for patients with no toxicity was 6.0cc (95% Cl 5.4cc-6.7cc) and 8.2cc (95% Cl 6.3cc-10.1cc) for patients with toxicity. The mean bladder 10cc for patients with no toxicity was 16.9Gy (95% Cl 16.3Gy-17.6Gy) and 18.4Gy (95% Cl 17.8Gy-19.1Gy) for patients with toxicity. The mean bladder D15cc for patients with no toxicity was 14.8Gy (95% Cl 14.0Gy-15.5Gy) and 16.6Gy (95% Cl 15.6Gy-17.6Gy) for patients with toxicity. The mean bladder V8Gy for patients with no toxicity was 44.0% (95% Cl 38.8%-49.2%) and 55.8 (95% Cl 46.0%-65.6%) for patients with toxicity. Results:

Conclusion: