ESTRO 2025 - Abstract Book

S3133

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

Exploratory outcomes correlated differences in confidence and visibility against patient age (range 36-71), BMI (range 18-48) and mean bladder volume (117-475ml).

Results: 149 fractions were imaged from 15 patients. Mean accuracy score was 3.36 on US-CBCT vs 3.31 on CBCT. Mean difference was 0.05, reflecting one additional correct choice per 100 fractions, neither clinically nor statistically significant (p=0.555). Mean difference in visibility was 0.12, reflecting one additional point on the 4-point Likert scale per 25 fractions (p=0.001). Mean difference in confidence was 0.07, reflecting one additional point per 43 fractions (p=0.048). In 69 fractions with poor CBCT visibility (1 or 0), the benefit of adding ultrasound was greater, with mean differences of 0.17, 0.25 and 0.33 in accuracy, visibility and confidence respectively. Ultrasound improved both visibility and confidence by a greater degree in patients of younger age, lower BMI and larger mean bladder volume (all p≤0.027); also for observers with less pelvic CBCT experience (p=0.035).

Conclusion: Ultrasound improved uterocervix visibility to a small degree but had no effect PotD selection accuracy.

Keywords: plan of the day, plan library, ultrasound

References: 1. Wang L, Alexander S, Mason S, et al. Carpe Diem: Making the Most of Plan-of-the-Day for Cervical Cancer Radiation Therapy. Pract Radiat Oncol 2023;13(2):132-147. DOI: 10.1016/j.prro.2022.11.005. 2. Mason SA, White IM, O'Shea T, et al. Combined Ultrasound and Cone Beam CT Improves Target Segmentation for Image Guided Radiation Therapy in Uterine Cervix Cancer. Int J Radiat Oncol Biol Phys 2019;104(3):685-693. DOI: 10.1016/j.ijrobp.2019.03.003.