In FLASH radiotherapy, a therapeutic dose is delivered in a very short time and at a much higher dose-rate than in conventional treatment protocols. In-vivo experiments during the past decade seem to indicate (at constant dose) a lesser sensitivity of healthy tissues to ionizing radiation when radiation is delivered in short and bright pulses, whereas the therapeutic effect on tumors remains unaltered. The very recent application of FLASH protocol radiation therapy to the first human patient [Bourhis 2019] opens the way to a high-potential innovation in cancer treatment. The mechanisms behind the FLASH effect have not however been completely elucidated yet, which indicates the need for a deeper insight into the basis of radiation toxicity on living tissues at disparate time scales, encompassing physics, chemistry, biology and physiology. The need of high dose delivered in a very short time makes a highenergy-laser-driven particle source the perfect candidate for novel experiments in this field.
We propose to use a laser-accelerated proton beam to study the biological response of in-vitro and in-vivo samples to irradiation at ultra-high dose rate and high dose per pulse. The short timescale over which TNSA protons are accelerated, enables irradiation with several nanoCoulombs of protons at the nanosecond time scale. This peculiarity of laser-driven sources enables reaching extremely interesting and seldom explored conditions. Indeed, TNSAaccelerated protons can be made relevant for biological applications, provided that a proper control on the spectrum and the beam divergence is implemented and a consistent dosimetry protocol is defined. We propose to use a set of permanent magnetic quadrupoles to shape and transport the proton beam to a biological sample placed in air outside the experimental chamber. The targeted irradiation conditions will allow us to study the effect of the complete therapeutic dose delivered in a single nanosecond pulse. Such experiment will enable exploring FLASH conditions with protons as well as testing a much shorter timescale than what is indicated for electrons and photons. The availability at the source of a polychromatic spectrum also eases the realization of a uniform depth-dose deposition, which makes laser-driven proton beams ideal for these investigations.
LULI2000 - S50-S51/2020