Isocentric precision study on Shanghai Proton Therapy Device 360° compact gantry

<bold>Background</bold>Shanghai Advanced Proton Therapy Device (SAPT) is the first domestic proton therapy demonstration device, and the gantry is an important part of the proton therapy device, with an isocentric accuracy of ±0.275 mm, which is superior to most of the international mainstream equipments and requires high motion positioning accuracy and reliability.<bold>Purpose</bold>This study aims to provide a reference for the impact of the gantry structure on the treatment accuracy of the gantry of proton therapy device under different rotation angle conditions.<bold>Methods</bold>Firstly, the development progress of the 360° gantry for SAPT located in the Shanghai Ruijin Hospital proton center was introduced, and its isocentric accuracy was presented in detail. Then, deformation analysis of the gantry center point was carried out through the static structural analysis module of ANSYS. Finally, the actual deformation was measured using a laser tracker, and the error sphere was plotted to determine the accuracy at the center point under typical working conditions and analyze the causes.<bold>Results</bold>The qualitative analysis of the isocentric accuracy during the gantry rotation process shows that the trend of simulation results is consistent with the measured data (correlation coefficient <italic>R</italic>² ≥ 0.92). The simulation predicts an overall isocentric accuracy of ±0.25 mm, while the measured result is ±0.275 mm, with a deviation rate &lt; 10%, which is superior to international mainstream equipment (typically &lt; ±1 mm). However, there is a certain deviation in the <italic>Z</italic>-axis direction (average deviation about 0.05 mm), which is attributed to mechanical installation errors not included in the simulation.<bold>Conclusions</bold>The simulation results of this study demonstrate that the stiffness, strength and stability of the gantry structure are at an excellent level, providing solid theoretical support for subsequent engineering applications. The successful development of China's first 360° gantry with ultra-high isocentric precision (±0.275 mm) represents not only a milestone in the localization of high-end medical equipment, but also achieves leading international level with innovative structure and cost advantages.