Background and Aims

Lately the research on FLASH effect pushed both the understanding of its scientific basis and the related accelerator technologies. This effort renewed the interest for electron beam, not only at low energy, as currently used for skin tumors or IORT, but also for Very High Energy Electron.

VHEE beams were suggested in the past as an alternative for deep seated tumors, but their complexity and cost kept them away from the clinical implementation. However, the recent developments in the field of compact electron acceleration at high intensity represent a promising perspective.

Methods

The SAFEST project aims to build a VHEE LINAC with FLASH capability, meant both for preclinical research and as prototype of a clinical device. The machine design is based on a conventional C-band LINAC with high gradient accelerating structure. The size (few meters) and the cost of the machine is compatible with clinical use.

SAFEST will be a flexible machine (70<Ebeam<130 MeV) with possibility of using both flat (100 cm²) or pencil beam field, with repetition frequency>100 Hz, and instantaneous dose rate >10⁶ Gy/pulse. The low magnetic rigidity of the beam allows for a small and fast active scanning system. Two experimental rooms are foreseen for preclinical and radiobiology studies.

To optimize the machine design and to estimate the expected clinical performances a dedicated TPS for VHEE, based on MC dose kernel, has been developed

Results

DVH for tumor and organs at risk has been obtained for different deep seated tumors. The SAFEST beam outperforms IMRT photon treatment, even using the same number of fields and without the possible enhancement due to FLASH delivery

Conclusions

The SAFEST approach represents a valid and realistic alternative to standard RT even at standard dose rate delivery. Furthermore, FLASH effect capability of such a beam opens new perspective in the RT of deep seated tumors