Single Room Proton Radiation Therapy

Abstract

Our proton delivery system is ready for clinical use. We describe the system, operation, and integration within our clinic. The superconducting synchrocyclotron - passive scattering accelerator contains beam line options to treat shallow or deep lesions with range adjustable by 1mm, and modulation up to 20cm. The accelerator is small and light enough to be placed on a gantry revealing a footprint slightly larger than a conventional room. The outer accelerator gantry aligns with an inner treatment gantry that houses applicators (14 or 25cm), field apertures and compensators. Gantry motion is limited to 190deg. Patient positioning and imaging are provided by a 6D robotic couch with 270 degrees of rotation and fixed x-ray and CBCT systems. The system is integrated with our medical record system and treatment planning. Dosimetric data (range, modulation, distal falloff, lateral penumbra) were generated from Monte Carlo calculations, confirmed by measurements. Neutron exposure was assessed by calculations and measurements. Dose rate and delivery efficiency was also assessed. We measured a maximum range of 32cm for small fields and 25cm for large fields. Modulation (SOBP) was found to be flat (±3% over the core portion). Distal falloff (80-20%) and lateral penumbra in air (80-20%) were no greater than 7mm and 4mm, respectively. Calculated/measured data were commissioned, from which generated plans were seamlessly transferred to patient information management system and subsequently, the MEVION console, including radiographic setup images. Neutron exposure was calculated and measured to be < 1mSv per Gy delivered, at 1m from isocenter for a 10x10 field. Dose rate ranged from 2-4 Gy/min. Usability and end-to-end testing revealed efficient treatment aspects (simple single console operation for beam generation), and inefficient aspects (frequent table movement due to the limited gantry range for treatment of > 1 field/day). Uptime is thus far extraordinarily high with rapid and stable beam-on operation. Treatment planning has demonstrated superior results compared with IMRT for established proton treatment sites (pediatric, H&N, CNS, etc.). The delivery capabilities and low neutron exposure affirm our desired use for pediatrics. Future treatment of ocular melanoma will include a proper optical alignment system; while lung treatment will utilize gating of the pulsed beam. Proton radiation therapy, till now, had been limited to facilities dedicating enormous space, resources, and of course expense. The success of this project launches the potential for proton radiation therapy at facilities starved for space (i.e., in heavily populated cities) or resources/finances (smaller academic institutions). We will continue to report on our clinical utility and solutions.