Partial demonstration of the fixed field fixed betatron tunes permanent magnet proton FLASH cancer therapy accelerator

The FLASH radiation delivers ultra-high dose in a much shorter time intervals significantly improving healthy tissues recovery. The radiation fractions are delivered in a part of a second (100 ms) as opposed to minutes in a standard cancer therapy and in far fewer fractions or even a single fraction at dose rates that are thousands of times higher. The proton FLASH therapy requirements of 40 Gy/s are to be compared to the dose of 0.01 Gy/s used in conventional radio therapy. The dose of 40 Gy/s in 100 ms for a volume of 1000 ml (10x10x10 cm) becomes a dose of 4 Grays delivered in 100 ms. The 3.8x10¹¹ protons or 60 nC is to be delivered in 100 ms equivalence of 600 nA. It is not yet clear why the high FLASH radiation spares the healthy tissue, but it looks like that radiochemical depletion of oxygen occurs inducing tissue radio resistance. This proposal, based on the previous successful 'CBETA' project [1, 2], removes limitations of the existing proton therapy facilities. It delivers protons with required energies in a very short time without changing the magnetic field. The fast cycling synchrotron with cycles repeating at frequency of f_REV~500Hz is made of fixed field small permanent magnets. Field variation is eliminated except in the fast transverse spot scanning. Variable magnetic field requirements for different energy settings are major limitations at any existing cancer hadron radiation therapy facility. The magnetic field adjustments within a very short time required for FLASH are very difficult to due to hysteresis. The cyclotron-based treatment centers required energy degraders as a single 230-250 MeV energy is extracted. At low energies only 1% of the initial beam is delivered to the patient. The beam size – emittance is always significantly enlarged as energy adjustments of the beam require passage through the degraders. We present permanent magnets built and installed for a part of the Fixed Field Alternating (FFA) gradient fast cycling synchrotron. The magnetic field measurements confirmed the predicted non-linear transverse magnetic field within a small beam aperture. Proton beam measurements through the arc magnet assembly in the NASA Research Laboratory at Brookhaven National Laboratory in the kinetic energy range between 10 MeV and up to 250 Mev will confirm the proposed principle.