Early Modulated Proton Therapy (EMPT) at FLASH Dose Rates: Proton Bursts Optimization, Stochastic Cooling, Spatial Intensity and Energy Modulations

Abstract

Abstract FLASH radiotherapy requires extremely high dose rate (DR > 40Gy/s) hence challenges prevalent external-beam technologies. To achieve FLASH DRs, proton accelerators are potentially the best candidates due to high kinetic energies for individual protons. However, as the major drawback of prevalent IMPT, the lengthy pencil-beam modulation is the key difficulty against FLASH DR. To resolve this, we relinquished pencil-beam modulation at treatment end, and proposed early modulation proton therapy (EMPT) for renovated proton synchrotrons. The EMPT procedures could be divided into 4 steps. First, proton beam (differentiated into bursts of certain sizes) for the entire radiotherapy treatment is injected into the synchrotron and accelerated. This pre-load design allows delivery time in microseconds, meeting the FLASH DR. Second, general stochastic cooling for primitive beam-bursts inside SSR using feedback loops. Third, spatial intensity modulation for each beam-burst inside SSR, the tumor-specific fine-tuned of step second. Fourth, energy modulations at exit pipelines, either by altering the magnetic field or implementing a voltage pulse gap. Early modulated proton bursts could stay in the SSR for 10-20min or longer without damping, thus EMPT fluences can be pre-loaded/generated and stored in SSR during patient setup. For each treatment plan, the TPS provides information on optimized burst size (minimal dose unit for EIMPT), burst numbers (calculated by prescription, tumor size), primitive energy, length of spread-out Bragg Peak etc. hence the early-modulation procedures could be performed inside SSR. Relinquishing pencil-beam in IMPT is fundamental to achieve FLASH DR. Implementing advancement of technologies in modern particle physics experiments, for the first time, EMPT was proposed, allowing pre-loaded, early modulated proton beams to satisfy FALSH Radiotherapy.