Application of cone-shaped scintillation detector for quality assurance in pencil beam scanning proton therapy systems

[Background] Pencil beam scanning (PBS) proton systems with a rotating gantry makes proton intensity modulation technology widely used for better protection of organs at risk, but it also brings greater challenges to the quality control of proton system. [Purpose] This study aims to verify the accuracy of an XRV-124 cone-shaped scintillation detector and to investigate its feasibility for use in PBS quality assurance (QA) procedures. [Methods] Firstly, according to the measurement principle of XRV-124, a single setup was implemented to measure the spot size, beam–X-ray coincidence, gantry angle, star-shot test, and mechanical accuracy simultaneously. Then, the spot size and beam – X-ray coincidence were determined at the isocenter using the XRV-124 for 70~240 MeV at increments of 10 MeV and at 30° increments for all gantry angles. The coincidence of the X-ray system and proton beam was evaluated in the X and Y directions of the International Electrotechnical Commission coordinate system (IEC). Finally, the spot size and coincidence results were compared with those of the widely used Lynx detector, whereas the gantry angle results were compared with those of the proton treatment console (PTC). [Results] The spot sizes obtained using the XRV-124 and Lynx are in good agreement within 0.10 mm for each energy, and the results show the same trend with a maximum deviation of 0.18 mm and 0.11 mm in the IEC-X and -Y directions, respectively. The gantry angles are less than 0.2° compared to those of the PTC. For the star-shot test, the average 3D and 2D distances from the isocenter are 0.4 mm and 0.2 mm, respectively, meets the quality control requirements. The QA items can be completed in 90 min. [Conclusions] This method of this study has been successfully applied to the QA of Varian ProBeam proton radiotherapy system in Hefei ion medical center, indicating that XRV-124 cone-shaped scintillation detector can be widely used in the same type of proton radiotherapy system to improve the QA efficiency and reduce the human error caused by frequent positioning. © 2024 Science Press. All rights reserved.