High Gradient Accelerating Structure for Low Energy Protons

Proton and carbon radiotherapy systems have demonstrated significant advantages in clinical efficiency and reduced toxicity profiles for many types of cancers, however the high cost of the accelerators and poor capability to manage moving tumors are the limiting factors preventing hadron therapy from becoming the standard of care for a wider range of patients. Developing a high gradient linear accelerator capable of fast and efficient tumor tracking and treatment through the 4D spot scanning technique would offer a promising approach to smultaneously reduce the cost and improve the quality of the treatment. In response to this problem, RadiaBeam in collaboration with Argonne National Laboratory is designing a compact (~50 m) linac capable of accelerating carbon beams up to the energies of 450 MeV/u and protons up to 250 MeV that can adjust beam energy pulse-to-pulse at up to 1,000 pulses per second. During this Phase II project, we have developed a novel accelerating structure for protons and carbon ions operating at the first negative spatial harmonic and capable of providing >50 MV/m gradient. We have demonstrated the anticipated performance via electromagnetic, beam dynamics and transient thermal analysis. The accelerating structure is currently being tested and gradients up to 37 MV/m were demonstrated, temporarily interrupted by the COVID-19 epidemic. In Phase IIB we will transition the proof-of-principle prototype towards a market-ready product. We will upgrade the linac to a high repetition rate version that will allow acceleration at 1,000 pulses per second. A new robust cooling system will have the cooling channels inside the structure, instead of the currently used water jacket. Furthermore, we will apply a pulse compression mechanism to adapt the structure for the use with the commercially available klystrons, which will dramatically reduce the price of the system. We will test the structure with a 5 MW klystron that will be capable of achieving required gradients and duty factors. The success of this project will be a major milestone towards demonstrating the technical feasibility of the entire carbon-proton linac radiotherapy system. This represents an attractive commercial opportunity in the rapidly growing market segment of hadron radiotherapy. The success of this project will result in improved availability and affordability of highly-promising ion radiation therapy for a wider range of cancer patients.