ESTRO 2025 - Abstract Book

S4134

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2025

Conclusion: Thermoplastic masks markedly improved CT-MRI image fusion quality, reducing variability in CTV_LN delineation and enhancing target differentiation. RTTs played a pivotal role in optimizing patient positioning and managing challenges posed by WB-MRI sessions, balancing image quality with patient comfort. Incorporating thermoplastic masks into TMLI planning workflows supports precise target delineation and minimizes errors, highlighting their efficacy in multimodal imaging. This study is supported by grant AuToMI (GR-2019-12370739 funded by the Italian Ministry of Health).

Keywords: whole-body CT/MRI, image fusion quality, TMLI

3760

Digital Poster Factors contributing to repeated cone beam computed tomography (CBCT) during radiotherapy for prostate cancer patients Dawid Bodusz, Anna Myśliwiec, Iwona Dębosz-Suwińska, Wojciech Majewski, Jerzy Wydmański Radiotherapy Department, National Research Institute of Oncology, Gliwice Branch, Gliwice, Poland Purpose/Objective: In prostate cancer radiotherapy, volumetric imaging plays a critical role in ensuring the accurate positioning of the target volume and assessing the shape and location of surrounding critical organs. However, repeated imaging increases the cumulative radiation dose and extends the operational time of therapeutic devices. This study aimed to analyze the frequency and underlying causes of repeated CBCT verifications in prostate cancer patients. Material/Methods: The study retrospectively examined all CBCT verifications performed daily during radiotherapy in January 2024 for prostate cancer patients. All patients were instructed on the preparation protocol for radiotherapy, including bladder filling and rectal preparation. Data from 112 patients, involving a total of 1446 CBCT verifications, were analyzed. Cases of repeated imaging on the same patient on the same day were reviewed to identify the causes related to deviations in rectal or bladder preparation and the presence of intestinal gas. Results: Out of 1446 CBCT verifications performed, 302 (20.8%) were repeated due to inadequate patient preparation. The primary reasons were insufficient bladder filling (177 cases; 58.6%) and improper rectal filling (202 cases; 66.9%). Incorrect bladder volume was the sole cause in 77 cases (25.5%), while improper rectal filling (as the sole cause) was observed in 80 cases (26.5%). In 65 cases (21.5%) simultaneous improper filling of the rectum and bladder was identified. Among the 112 patients, 4 underwent repeated CBCT imaging more than 10 times during treatment, while 20 patients required 5–9 repeats. Each repeated imaging session, including patient positioning and image verification, consumed at least 10 minutes, resulting in a total more than 50 hours spent on repeated verifications in a single month. Introducing bladder volume assessments using ultrasound outside the therapeutic device could potentially prevent 77 repetitions, reducing machine utilization time at least 12 hours. Conclusion: Inadequate bladder and rectal preparation are the primary contributors to repeated CBCT imaging during prostate cancer radiotherapy. The implementation of ultrasound-based bladder volume assessments outside the therapeutic device could possibly reduce the need for repeated imaging and enhance the efficiency of treatment workflows. Extending ultrasound assessments to include rectal preparation may further optimize resource utilization.

Keywords: prostate, radiotherapy, bladder