Cancer is one of the leading causes of death worldwide. Several therapies are adopted for its treatment, with photon radiotherapy (RT) generally being the preferred option. Surgery, chemotherapy and conventional radiotherapy can in fact intervene in 65% of cancer cases, but leave a significant number of patients with untreatable tumours such as radio-resistant tumours. So far, apart from photons, only protons have been implemented as an alternative radiotherapy for such tumours. The use of very high energy electron beams (VHEE) (100-200 MeV) has been suggested in the literature, but the required accelerators are bulkier and more expensive than standard photon devices, with only limited advantages over protons or other heavy ions. The VHEE treatment planning system combining accurate Monte Carlo (MC) simulation with simple modelling of the FLASH effect (sparing healthy tissue at very high doses) compared with conventional RT show that FLASH therapy with VHEE beams of 70-130 MeV could be a viable alternative to standard RT, allowing better sparing of healthy tissue surrounding the tumour, within the framework of an affordable technological development. The first results obtained with a preliminary device are encouraging, and a new prototype is about to be tested. The final goal is the construction of a Treatment Planning System (TPS) capable of optimising the beam intensity and spatial distribution of small radiation fields in the FLASH regime by evaluating the best instantaneous intensity of a typical Flash pulse with a spatial resolution of ~ mm. Evaluations will be performed comparing treatment plans for conventional RT with VHEE FLASH treatment plans.
The validation of the FLASH effect and its implementation in cancer therapy will be one of the main research topics for medical applications in physics in the coming years. The growing number of experiments and the increased interest on the part of the medical community, motivated by the significant benefits it could bring to the quality of treatment, will require an enormous effort on the part of researchers in fundamental sciences such as physics, chemistry and medicine. In this perspective, organising a TPS for beam optimisation suitable for use and management in clinical practice will be considered an indispensable achievement to justify the construction of a clinical apparatus based on VHEEs. So far, the beam intensities required to achieve FLASH rates are so high that standard monitoring and dosimetry techniques used in clinical routing fail to provide accurate estimates of absorbed dose and its instantaneous rate per pulse, given the high temporal resolution required. This problem will be addressed in the context of IORT since low energy electron beams with dose rates >40 Gy/s are already available and most effects due to FLASH are expected to have a small dependence on the energy and type of radiation used. In addition, the project will explore the possibility of creating treatment plans that have never been carried out before and comparing the results with those of conventional RT. If proven successful, the project could initiate new investigations into the possibility of using the same physical principle in other fields of application, such as dosimetric measurements for high-energy linear accelerators and beam monitoring in various radiation physics applications.