S2702
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
setup reproducibility between SGRT and tattoo-based positioning. The SGRT system utilised was IDENTIFYTM V3.0 (Varian Medical System, Palo Alto, USA). Each patient received 15 treatment sessions, with the first 8 fractions using a tattoo-based setup and the remaining 7 fractions using SGRT. Six-degree-of- freedom (6DoF) image registration (IR) and residual SGRT shifts were recorded for all sessions. Wilcoxon Signed-Rank Test and Levene’s test of equality of variance were performed to compare the accuracy and reproducibility of the two setup methods. Results: All patients were female, with a median age of 56.5 years (Range: 35–80). Eight received right-sided, 19 left-sided, and 3 bilateral breast or chest wall radiotherapy. In total, 432 fractions were analysed.Comparing SGRT residual and IR shifts for the first 8 days, a Wilcoxon-signed rank test revealed a statistically significant reduction in the setup errors derived by SGRT versus tattoo-based IGRT in the Ant/Post (Z=-6.540, p<0.001), Sup/Inf plane (Z=-6.475, p<0.001) and pitch axis (Z=-3.781, p<0.001). No statistically significant difference was observed in the left/right plane, roll and yaw axes (p>0.05) (Table 1).Levene’s test of equality of variances revealed that SGRT had significantly lower variability in vertical (p = 0.023) and longitudinal (p = 0.034) directions compared to tattoo-based setups, indicating greater setup reproducibility. A borderline difference was observed in roll (p = 0.052), favouring SGRT. No significant differences were observed in the lateral, rotation, or pitch directions (p > 0.05) (Table 2). These findings suggest that SGRT improves setup consistency primarily in the translational axes.
The rectal tube catheter represents an innovative, patient specific intervention for cases where natural gas passage is not possible. It improves efficiency, prevents prolonged delays, and reduces patient frustration, while supporting continuity of treatment. Natural passage remains effective for many patients, but catheter availability provides an essential alternative when natural passage fails. Its use can be expanded to pretreatment too in reducing planning delays due to rectal gas. Larger studies are warranted to establish its broader role in EBRT and HDR brachytherapy. References: 1. Chen Y, et al. Large rectal volume variations; planning on empty rectum recommended. Radiother Oncol. 2010;97:65–72.2.Sasaki R, et al. Full-arc VMAT least affected by rectal gas; partial arcs showed larger dose distortions. Rep Pract Oncol Radiother. 2020;25:451–458.3.Vergalasova I, et al. Removal of rectal gas in gynecologic HDR brachytherapy reduced rectum/bladder D2cc. J Appl Clin Med Phys. 2021;22:345–354.4.Bristow R, et al. Daily bowel prep caused low patient anxiety; education on prep important. J Med Imaging Radiat Sci. 2018;49:123– 130.5.Wootton L, et al. Gas-release balloon improved workflow efficiency. Radiother Oncol. 2012;104:111– 116. Keywords: IGRT, Reproducibility, Rectal Gas management Comparative Evaluation of SGRT and Tattoo-Based Setup for Enhancing Accuracy and Reproducibility in VMAT Breast Cancer Treatment. Yan Ru Chia 1 , Eric Pei Ping Pang 1,2 , Felicia Sing Yin Chow 1 , Muhammad Fairuz Jumee 1 , Li Hoon Lim 1 1 Department of Radiation Oncology, National Cancer Centre Singapore, Singapore, Singapore. 2 Oncology Academic Clinical Programme, Duke-NUS Graduate Medical School, Singapore, Singapore Purpose/Objective: Tattoo markings are the standard of care for ensuring setup reproducibility for patients undergoing radiation therapy [1]. With growing interest in the psychosocial impacts of tattoos [2]—particularly among breast cancer patients— surface guided radiation therapy (SGRT) has emerged as a potential alternative. We aim to evaluate whether SGRT-based setup results in better setup accuracy and reproducibility for Volumetric Modulated Arc Therapy (VMAT) breast RT compared to tattoo-based setup. Material/Methods: Thirty VMAT breast patients were included to compare Digital Poster 740
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