S1509
Interdisciplinary - Quality assurance and risk management
ESTRO 2026
Conclusion: The combined use of prospective and retrospective risk analyses offers a deeper understanding of the specific risks associated with SGRT and DIBH. This integrated approach optimizes risk management, strengthens human, organizational and technical defences, and supports continuous safety improvement in radiotherapy. Keywords: Patient safety, risk analysis, SGRT
Results: Magnetic field strengths, Figure 1, ranged from 1.3- 12.5 gauss, Table 1, at clinically relevant locations, with measured values closely matching simulation predictions. The 5-gauss line extends approximately 8 meters LEFT-RIGHT, 4 meters ANT-POST and SUP-INF directions from the synchrocyclotron isocenter.
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Can Proton Accelerators with High Magnetic Fields Coexist with Modern Radiotherapy Technologies? Serdar Charyyev 1 , Xunjie Yu 2 , Yu Gao 1 , Zhuoran Jiang 1 , Gregory Szalkowski 1 , Lei Wang 1 , Lawrie Skinner 1 , Murat Surucu 1 , Yong Yang 1 1 Radiation Oncology, Stanford University, Palo Alto, USA. 2 Physics and Applied Mechanics, Mevion Medical Systems, Littleton, USA Purpose/Objective: The proton therapy field is experiencing a dramatic technological shift, with over 50% of new proton centers in the US incorporating ultra-compact systems that offer reduced facility footprint and construction costs. As these compact proton therapy systems are increasingly installed adjacent to existing radiotherapy modalities within multi-room cancer centers, understanding electromagnetic compatibility becomes critical. Purpose of this work is to evaluate the magnetic field and RF interference from a compact 10T superconducting synchrocyclotron, Mevion S250- FIT, on adjacent radiotherapy systems and assess potential impacts on dosimetry and image quality. Material/Methods: Systematic magnetic field mapping was performed around a Mevion S250-FIT proton therapy vault using calibrated gaussmeters at 23 measurement points. Simulation-based isomagnetic field predictions were validated against measured values. Pre- and post- magnet ramp-up assessments were conducted in adjacent ViewRay MR-Linac and CyberKnife vaults. For ViewRay, an MR-conditional 2D ion chamber array measured central-axis dose and beam profiles at multiple gantry angles (0°, 90°, 270°) and field sizes (4×4 to 20×24 cm²), while a MagPhan RT 820 phantom evaluated geometric distortion, SNR, and uniformity under three conditions: baseline, post-ramp without RF, and post-ramp with RF activated. For CyberKnife, a high-resolution CMOS detector assessed dosimetric performance using MLC and fixed collimator fields at 0° and 90°, with orthogonal kV imaging evaluated for targeting accuracy. Quantitative analysis included beam flatness, symmetry, and positional accuracy to detect magnetic/RF interference effects.
For ViewRay, central-axis dose differences were ≤0.2%, field size variations <0.1 mm, and profile flatness/symmetry changes ≤0.1%. Image quality metrics including geometric distortion (<1.5 mm at 350 mm diameter), SNR (43.6), and spatial resolution showed no degradation with synchrocyclotron energized and RF activated. For CyberKnife, central- axis dose variations were ≤0.001 cGy/MU, field sizes consistent within 0.05 mm, and targeting accuracy maintained within 0.2 mm offset. All parameters remained within institutional tolerances. Conclusion: Compact superconducting synchrocyclotrons can be safely installed in multi-vault radiotherapy facilities without compromising adjacent systems when proper facility planning is implemented. The 5-gauss line extends only into the proton vault maze, requiring considerations for cardiac devices, but not affecting other patient treatment areas. The self-shielded design provides adequate magnetic containment for typical clinical scenarios.
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