Medical research with laser-driven proton beams at Eli-Beamlines: rationale and preliminary results

Radiotherapy with charged particles has become an increasingly common treatment modality, because of several advantages it offers compared to photons. Clinical facilities employing proton beams produced from synchrotron, cyclotron or linac accelerators have to face high installation and running costs (> 200M€), which considerably limits their diffusion. Hence, innovative solutions are sought, such as the idea to exploit beams produced by the interaction of high-power lasers with appropriate targets in order to obtain higher performances at lower costs compared to the conventional accelerators facilities. The design of laser-based medical accelerators is currently the object of a large EU-funded project at the ELI (Extreme Light Infrastructure) facility in Prague, CZ, as well as the aim of the INFN-funded project PLASMA_MED (Proton LASer-driven beam transport, diagnostic and Medical Applications). The ultra-short (from fs to ps) and ultra-intense nature of the laser-target interaction gives rise to ultra-high dose rates (exceeding (10^9 Gy/s) proton beams, many orders of magnitude larger than the ones used in the usual radiotherapy working regime. Establishing laser-driven proton beams for medical use requires the study of their radiobiological properties, taking into account the strong dependence of the biological effects from the spatio-temporal physical pattern of energy deposition events. Therefore, the kickoff for radiobiological investigations and, in general for multidisciplinary applications, will be given once the laser-accelerated proton beam transport, selection and dosimetry system is up and running. A beam transport line (BTL) prototype able to deliver laser-generated proton beams with optimized properties and adequate repetition rates has been designed and tests are undergoing. The prototype of a major component of the whole BTL system, the Energy Selector System (ESS), able to control and select the laser-driven proton beams has already been developed and experimentally tested at the Tandem, LNS-INFN facility Catania, Italy, LNL-INFN facility Legnaro (PD), Italy and at the Taranis laser facility Queen???s University, Belfast (UK). Monte Carlo simulations were carried out to characterize the device. Preliminary and promising results are available and will be here illustrated.