S1788
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
(RBE) model for proton therapy based on all published in vitro cell survival data. Phys Med Biol 2015;60:8399– 416. Keywords: Proton therapy,Brainstem toxicity,Fossa posterior
Mini-Oral 4998
Comprehensive commissioning of the world’s first ultra-compact proton therapy system with upright patient positioner and CT Serdar Charyyev 1 , Vivek J Maradia 1 , Zhuoran Jiang 1 , Veng Jean Heng 1 , Cynthia Chuang 1 , Lloyd Kamole Ghomsi 1 , Kaan Dere 2 , Lawrie Skinner 1 , Bin Han 1 , Nataliya Kovalchuk 1 , Susan M Hiniker 1 , Yuan James Rao 1 , Billy W Loo Jr 1 , Lei Xing 1 , Murat Surucu 1 , Yong Yang 1 1 Radiation Oncology, Stanford University, Palo Alto, USA. 2 Natural and Computational Sciences, Minerva University, San Francisco, USA Purpose/Objective: To report the comprehensive commissioning of the ultra-compact upright proton therapy system. Material/Methods: The system (Fig. 1A) comprises a synchrocyclotron- based compact accelerator with fixed horizontal beam, scanning magnet with x-y coils nested that provides 6 mm/ms scan speed in both planes, boron carbide energy shifter plates at the nozzle with fastest possible energy change time of 50 ms, adaptive aperture for dynamic field collimation, upright patient positioner (UPP) with six-degree-of-freedom, and diagnostic quality upright fan-beam CT. TPS commissioning (Fig. 1B) was performed through measurements of integral depth doses (IDDs), spot profiles in air, and absolute dose calibration. Validation included spot position accuracy, spot profiles in water, IDDs for different energies, field size and penumbra, absolute dose for pristine Bragg peaks and spread-out Bragg peaks (SOBPs), and patient-specific QA using 2D detector arrays. For the upright system, mechanical and radiation isocentricity, laser alignment, adaptive aperture and nozzle positioning accuracy and leakage were tested. UPP assessments included positioning accuracy (vertical, longitudinal, lateral, pitch, roll, yaw), repeatability, sag, backrest angle, rotation speed, and treatable volume. CT image quality was characterized through HU uniformity, spatial resolution, low-contrast performance, spatial integrity, CT number accuracy, and CT-RSP calibration. Comprehensive safety testing validated motion interlocks, warning lights, collision prevention, emergency stops, and patient monitoring.
Results: Commissioning results (Table 1) showed beam dosimetry TPS agreement within 0.3-0.4 mm for range (R90/R80) across 34.1-227.1 MeV, with distal falloff within 0.2 mm. Spot size in air showed TPS agreement better than 0.2 mm at 227.1 MeV. Spot position accuracy was within 0.5 mm (mean inplane), 0.1 mm (mean crossplane) over 20 × 20 cm ² scan field. Spot size in water ( σ x: 4.17-12.71 mm, σ y: 4.1-12.44 mm) demonstrated TPS agreement within 0.2 mm. Absolute dose calibration yielded 0.0600±0.0002 cGy/MU with TPS agreement better than 0.5%. Absolute dose validation for single layers and SOBPs showed agreement within 3%. Patient-specific QA yielded 97.2- 99.8% (3%/3mm) and 91.4-97.6% (2%/2mm) gamma pass rates. Upright CT demonstrated CT number accuracy within tolerance for all tissue-equivalent materials, HU uniformity of 13.2 HU, CNR of 0.95, spatial resolution of 7.0 lp/cm, and spatial integrity of 0.67 mm. All safety systems functioned properly. Conclusion: The first ultra-compact upright proton therapy system was successfully commissioned with dosimetric accuracy comparable to conventional systems, submillimeter geometric precision, diagnostic quality imaging, and comprehensive safety validation. Keywords: upright, Mevion S250-FIT, proton therapy Poster Discussion 5015 pyRadPlan - an AI-ready open source treatment planning toolkit Florian Leininger 1,2 , Tobias Becher 1,2 , Lina Bucher 1,2 , Jennifer Hardt 1 , Tim Ortkamp 1,3 , Victoria Santiago 1,2 , Samir Schulz 1,2 , Goran Stanic 1,2 , Niklas Wahl 1 1 Medical Physics in Radiation Oncology, German Cancer Research Center, Heidelberg, Germany.
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