S2700
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
majority were conducted in the USA (n = 19) and Europe (n = 18), with fewer from Australia (n = 5) and Asia (n = 2). Conclusion: This review mapped the current evidence on real-time intra-fraction prostate motion monitoring during radiotherapy. Systems such as electromagnetic transponders (EMS), kilovoltage intrafraction monitoring (KIM), transperineal ultrasound (TPUS), and MR-guided radiotherapy (MRgRT) provide viable motion management strategies, though each has technical limitations that restrict widespread implementation. The findings highlight the importance of intra-fraction motion management, particularly for hypofractionated and SABR protocols, and underscore the need for continued technological development and comparative evaluation for clinical integration. Keywords: Prostate SABR, Intra-fraction imaging, IGRT Digital Poster Highlight 630 A Comparative Study of Patient Positioning Accuracy between Two Types of Immobilization Devices in Proton Beam Therapy for Prostate Cancer. Nichakon Rakkiet, Thitirat Tienghongsakul, Weerapat Wo-onsri Division of Radiation Oncology, Department of Radiology, King Chulalongkorn Memorial Hospital, The Thai Red Cross Society, Bangkok, Thailand Purpose/Objective: Prostate cancer is one of the most common malignancies worldwide, and precise radiation delivery is essential to maximize tumor control while minimizing exposure to surrounding organs. Effective patient immobilization plays a critical role in maintaining setup accuracy during proton therapy. This study aimed to compare the HipFix thermoplastic system and the Vacuum Bag (VB) in terms of setup accuracy (six degrees of freedom) and setup time. Material/Methods: Thirty prostate cancer patients treated with intensity- modulated proton therapy (IMPT)at a single center were retrospectively analyzed—15 immobilized with HipFix and 15 with VB(Figure 1.)
between July 2022 and April 2025. Setup errors were evaluated using cone-beam CT image guidance, including translational (anterior–posterior [AP], superior–inferior [SI], left–right [LR]) and rotational (pitch, roll, yaw) deviations. Translational and rotational Total Vector Errors (TVE) were calculated to represent overall positional deviations.Systematic ( Σ ) and random ( σ ) errorswere calculated for each axis. Setup time was recorded from the start of patient positioning to completion of verification. Independent t-tests were used for comparison (p < 0.05). Results: A total of 577 CBCT images from 30 patients were analyzed in this study.Translational accuracy was comparable between the two systems (p > 0.05). However, VB demonstrated significantly better rotational stability, particularly in the roll (0.7° vs. 0.5°, p = 0.04) and yaw (0.6° vs. 0.4°, p = 0.04) axes, as shown in Figure 2.
Moreover, VB showed superior rotational TVE (1.2° ± 0.3 vs. 1.0° ± 0.2, p = 0.01). Both systems showed similar translational systematic and random errors (0.1–0.3 cm/°), while VB achieved slightly improved rotational precision (roll 0.3° vs. 0.4°). Setup times
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