Technical commissioning of the spot scanning system in Shanghai Proton Therapy Facility

BackgroundIn the field of particle therapy, the method of pencil beam scanning is of great potential for clinical application, now and in the future.
PurposeThe authors made strong effort to develop a spot scanning system for Shanghai Proton Therapy Facility. Design parameters and basic layout of the system are introduced.
MethodsFunctionalities and specifications of crucial devices are described in detail. Most of the devices in the system were designed in house by the authors themselves, including scanning nozzle, scanning magnets and their power supplies, beam monitors, irradiation control modules and safety interlock modules. During the technical commissioning stage in the fix beam room, the spot scanning system was tested and verified.
ResultsUnder conditions of the maximum dose rate and minimum dose rate, a) repeatability of the single spot dose is less than ±0.1%; b) nonlinearity of the single spot dose is less than ± 0.1%; c) FWHM for spot size in air at isocenter varies from 8mm to 12mm for full energy, consistent with the design values; d) lateral dose distribution achieves a flatness of less than 2% for multiple proton energies.
ConclusionAccording to the results of technical commissioning, the spot scanning system is capable of producing a prescribed 3D dose distribution for target tumor successfully.