S2113
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
https://doi.org/10.1016/j.ijrobp.2023.01.004 Keywords: MRI guidance, shuttle transfer, cervical cancer
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Results: Comparison of consecutive shifts showed that the median DSC (MDA) of the external contour, encompassing the area where patients would be irradiated, was 0.99 (0.5 mm) for MRI 1–2, 0.99 (0.9 mm) for MRI 2–3, and 0.99 (0.9 mm) for MRI 3–4, suggesting high stability of patient positioning. Cervix, uterus, bladder, intestine, and rectum demonstrated high organ variability between MRI scans (Figure 2). Median MDA values observed for MRI 1–2/MRI 2– 3/MRI 3–4 were 2.2/2.8/1.8 mm for the cervix, 3.6/4.2/3.7 mm for the bladder, and 1.6/1.4/1.7 mm for the rectum.
Commissioning of a nonclinical surface-guidance imaging system with an integrated 6-DOF couch on an O-ring linear accelerator. Douglas Bollinger 1 , Brook Byrd 1 , Jufri Setianegara 1 , Taoran Li 1,2 , Sophie Rooks 1 , Jack Shaw 1 , Maksym Sharma 1 , Steven Philbrook 1 , Kevin Teo 1 1 Department of Radiation Oncology, Penn Medicine, Philadelphia, USA. 2 Medical Affairs, Varian, Palo Altor, USA Purpose/Objective: O-ring linacs allow for a streamlined and efficient clinical workflow with potentially improved CBCT image quality. However, their closed-bore nature necessarily restricts the range of allowable FOVs and camera arrangements for SGRT systems (1). In this work, we commissioned and investigated the achievable optical accuracy of a nonclinical SGRT system on an O-ring linac. Material/Methods: Commissioning measurements of the IDENTIFY V5.0 SGRT system (Varian Medical Systems) included functionality checks of the SGRT’s optical characteristics, measurements of static localization accuracy and reproducibility, dynamic localization accuracy, SGRT vs CBCT isocentricity, and end-to-end tests as per TG-302’s recommendations (2). Static localization accuracy and reproducibility was assessed by capturing a static surface over 10 repetitions. Shift localization accuracy was assessed by introducing 0.1- 7.0cm translations and 0–3° rotations incrementally and assessing SGRT measurements of a planar calibration phantom vs nominal shift. End-to-end tests were performed with anthropomorphic head and body phantoms with the surfaces contoured and sent from TPS to the SGRT workstation. CBCT vs. SGRT isocentricity and shift correspondence tests were performed by imaging these phantoms, applying clinically relevant shifts, and assessing the discrepancies between the measured CBCT vs. SGRT shifts. Results: All functionality tests were satisfactory. Repeated static surface captures showed no translational fluctuations, with maximum differences of 0.30° and 0.10° in yaw and pitch, respectively. SGRT recorded shifts showed maximum translational discrepancies of 0.4 mm, 0.3 mm, and 0.1 mm in the vertical, longitudinal, and lateral axes respectively vs. nominal couch shifts (Figure 1). The corresponding rotational discrepancies
Conclusion: The study demonstrated that high stability in the external outline of the female pelvic region can be achieved while using a shuttle-based workflow for MRI-guided adaptive particle therapy. Physiological organ motion remained the main source of variability and was only marginally influenced by the shuttle transport. Optimizing bladder preparation protocols may further enhance reproducibility. Future studies may apply the shuttle workflow for other anatomical regions. References: [1] Albertini F, Matter M, Nenoff L, et al. Online daily adaptive proton therapy. Br J Radiol 2020;93(1107):20190594. https://doi.org/10.1259/bjr.20190594[2] Pham TT, Whelan B, Oborn BM, et al. Magnetic resonance imaging (MRI) guided proton therapy: A review of the clinical challenges, potential benefits and pathway to implementation. Radiother Oncol 2022;170:37–47. https://doi.org/10.1016/j.radonc.2022.04.002[3] Arians N, Lindel K, Krisam J, et al. Treatment Tolerability and Toxicity of Postoperative Proton Beam Therapy for Gynecologic Malignancies: Results of the Prospective Phase 2 APROVE Trial. Int J Radiat Oncol Biol Phys 2023;116(4):825–836.
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