ESTRO 2025 - Abstract Book

S4108

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

ESTRO 2025

References: Pötter R, Tanderup K, Kirisits C, de Leeuw A, Kirchheiner K, Nout R, et al. The EMBRACE II study: The outcome and prospect of two decades of evolution within the GEC-ESTRO GYN working group and the EMBRACE studies. Clin Transl Radiat Oncol 2018;9:48–60. Shah M, Agarwal S, Agarwal R, Subramanian B, Gupta S, De S, Mishra S. Observational study of cone beam computed tomography based interfractional urinary bladder filling variation during image guided radiation therapy in pelvic malignancies. J Cancer Res Ther. 2021 Jan-Mar;17(1):152-156. Nishioka K, Shimizu S, Kinoshita R, Inoue T, Onodera S, Yasuda K, et al. Evaluation of inter ‐ observer variability of bladder boundary delineation on cone ‐ beam CT. Radiat Oncol 2013;8:185.

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Digital Poster Review of patient verification protocols for treatment delivery of cardiac SABR in patients with Ventricular Tachycardia Marina Khan 1 , Georgios Ntentas 2 , Saima Naz 1 , Meera Patel 1 , Michelle Stenson 2 , Shahreen Ahmad 3 1 Radiotherapy, Guys & St Thomas' NHS Foundation Trust, London, United Kingdom. 2 Medical Physics, Guys & St Thomas' NHS Foundation Trust, London, United Kingdom. 3 Clinical Oncology, Guys & St Thomas' NHS Foundation Trust, London, United Kingdom Purpose/Objective: Ventricular Tachycardia (VT) is a potentially life-threatening condition for which SABR is an innovative treatment option [1] . Cardiac SABR (cSABR) for this benign condition is indicated after all conventional treatments have failed. We have been treating these patients at our institution since 2021. We devised an image review process based on existing protocols for thoracic malignancies and advice from other cSABR treating centres. Here we evaluate the treatment verification process at our centre. Material/Methods: Our current IGRT process uses a 3-minute 3D-CBCT (607.5 mAs), followed by a post correction 4D-CBCT (672 mAs) and a mid-treatment 2-minute 3D-CBCT (405 mAs. The 2-minute and 3-minute CBCTs were optimised in-house specifically for this group of patients, using the methods from Khan et al 2022 [2] . The 4D-CBCT is a Varian™ default protocol. All images were independently assessed offline by 3 therapeutic radiographers (RTTs) using the scoring tool below (Figure 1).

Results: Thirteen patients were referred for cSABR. Two patients did not receive treatment. CBCT images were evaluated for eleven patients. The three RTT’s scored consistently apart from patient 4 whose 4D-CBCT was scored higher by 1 RTT. The 4D-CBCT images were poor quality, and RTTs were unable to complete image registration for five patients. In the remaining six patients image registration was possible (all scored 2) despite poor image quality. The 3-minute scan was scored highest, with seven patients scoring at least 3, with the 2-minute CBCT scoring in the middle (Figure 2). No patients scored below 2 on the 2-minute CBCT.