Pyramid Technical Consultants, Inc.

A review.Particle therapy is a good example of technol. transfer from high-energy physics to medicine.Using beams of protons or carbon nuclei, a high dose of radiation can be delivered to a cancerous tumor while minimizing the dose to surrounding healthy tissue.A particle-therapy treatment involves making a diagnosis, agreeing the use of radiation therapy and then creating a treatment plan.By the end of 2009 about 78000 patients had been treated by particle therapy since its inception in 1954, and there were 30 centers in operation, with another 15 or so under construction.However, the cost of a new facility is in the region of $100-200m.Making particle therapy as widely available as X-ray radiotherapy will require the cost to be reduced by about a third, and it would be preferable to fit the equipment into existing hospital radiotherapy facilities.Fortunately, several companies and research groups are pursuing this goal.For now, the more conventional synchrotron- and cyclotron-based facilities are treating patients successfully and provide a wealth of medical data, plus com. opportunities for companies that provide the accelerator components, beam diagnostics, control systems and buildings.

Background: This study aims to present the feasibility of developing a synchrotron-based proton ultra-high dose rate (UHDR) pencil beam scanning (PBS) system. Methods: The RF extraction power in the synchrotron system was increased to generate 142.4 MeV pulsed proton beams for UHDR irradiation at ~100 nA beam current. The charge per spill was measured using a Faraday cup. The spill length and microscopic time structure of each spill was measured with a 2D strip transmission ion chamber. The measured UHDR beam fluence was used to derive the spot dwell time for pencil beam scanning. Absolute dose distributions at various depths and spot spacings were measured using Gafchromic films in a solid-water phantom. Results: For proton UHDR beams at 142.4 MeV, the maximum charge per spill is 4.96 ± 0.10 nC with a maximum spill length of 50 ms. This translates to an average beam current of approximately 100 nA during each spill. Using a 2 × 2 spot delivery pattern, the delivered dose per spill at 5 cm and 13.5 cm depth is 36.3 Gy (726.3 Gy/s) and 56.2 Gy (1124.0 Gy/s), respectively. Conclusions: The synchrotron-based proton therapy system has the capability to deliver pulsed proton UHDR PBS beams. The maximum deliverable dose and field size per pulse are limited by the spill length and extraction charge.