Research status and prospect of tumor therapy by using laser-accelerated proton beams

Proton radiotherapy is one of the most important modalities to treat cancers, which attracts a lot of attention for that it can precisely target the tumor with reduced side effects. However, due to the financial pressures of constructing and maintaining a proton radiotherapy center, nowadays this treatment method is not wildly available worldwide. In this context, the novel proton acceleration techniques based on high-power laser facilities are believed to become a competitive acceleration method, mainly for the advantages of compact size and low complexity. Meanwhile, the laser accelerated protons own some special features like broad energy spectrum, ultra-short pulse duration and ultra-high peak current, which would favor the research about radiobiological effects under ultra-high dose rate radiotherapy. As for laser-accelerator-based proton radiotherapy, the fundamental challenge nowadays lies on the proton energy that can be achieved (<100 MeV), which is not enough to completely meet the needs of human treatments, while we have seen the potential of the advanced target structure and cascaded acceleration to enhance the beam energy. Besides, quantities of in vitro and in vivo biological experiments have been carried out, benefiting from the adjunct development of beam transportation elements that are suitable for laser-accelerated protons, and biological phenomena that differ from the case of using conventional proton beams have been observed. Furthermore, compared with the standard dose rate radiotherapy, there are evidences showing the significant advantages of ultra-high dose rate radiotherapy in regulating immunity, which paves the way to a multidisciplinary field of radiobiology, immunology, and advanced acceleration technology, where there should be a place for laser accelerators. Additionally, the past two decades have witnessed the worldwide booming developments of petawatt class laser facilities, accompanied by the increasing peak power and declining cost per petawatt. This progress might promote the clinical use of laser accelerators in the future. In the past few years, we have carried out theoretical and experimental research concerned with laser proton acceleration, beam transportation, radiobiology and immunology based on the platforms of the Compact Laser Plasma Accelerator of Peking University and Beijing Laser Acceleration Innovation Center, in order to investigate the availability and probable advantages of tumor therapy by using laser-accelerated proton beams. In this review, the research status from these aspects at home and abroad is introduced, and the progress as well as problems is discussed especially in the dose delivery and biological effects. Finally, the future development of laser-accelerator-based proton therapy is discussed and prospected.