ESTRO 2024 - Abstract Book

S2467

Clinical - Urology

ESTRO 2024

on the 1.5T MR-Linac (NCT04075305) 7,8 . Prostate SBRT has been successfully delivered to many patients treated within MOMENTUM 9 .

The overall treatment time (OTT) of prostate SBRT is variable 3,4,10 and despite the aim to reduce toxicity in these men there is little data to depict how overall treatment time (OTT) effects toxicity.

This study aims to use data from the MOMENTUM repository to answer the question; does OTT impact toxicity when treating prostate cancer with SBRT?

Material/Methods:

Patients receiving 36.35 Gy to 40 Gy in 5 fractions for localised prostate cancer within MOMENTUM were included. ADT was the only adjuvant therapy permitted. Men were grouped according to OTT with Group A receiving treatment three times a week (EOD) or more frequently and Group B receiving treatment twice a week or less frequently. Patient characteristics, PSA, physician-reported gastrointestinal (GI) and genitourinary (GU) toxicity using Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 and patient reported outcomes (PROs) were collected at baseline and at 3, 6, 12, and 24 months after the radiotherapy. It is assumed that centres enter all higher grade CTCAE toxicities in to the MOMENTUM database.

PROs were scored using the European Organization for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire (QLQ)-C30 and EORTC QLQ-PR25.

A mixed model analysis was used to compare how scores changed and differed between Group A and Group B. For EORTC QLQ-C30 and QLQ-PR25 scores the difference in change over time between groups were calculated with a 95% confidence interval (CI). If the CI passes 0 any differences were deemed statistically insignificant.

Significant changes in EORTC QLQ-C30 scores were then interpreted using minimally important difference (MID) guidelines 11 .

Results:

862 patients were included; 161 patients in Group A and 701 patients in Group B. The mean OTT was 10.5 days (SD=1.84) in Group A and 15.4 (SD=4.08) in Group B. The most used fractionation schedule was 36.25 Gy in 5 fractions, prescribed in 693 (80.4%) patients. No grade 4+ GI toxicities were reported. There was one grade 3+ GU toxicity recorded post radiotherapy: urinary retention occurring at 3 months post-radiotherapy. 8 patients were recorded as experiencing a grade 2 GI toxicity by 24 months and 56 were recorded as experiencing a grade 2 GU toxicity by 24 months. This is likely an under representation due to lack of data capture.

Following SBRT on the MRL EORTC scores were very good in both groups with high functioning scores and low symptom scores (Figure 1).