Systematic analysis of alanine/EPR pellets for reference dosimetry with UHDR electron beams for FLASH radiotherapy

Advancements in radiotherapy techniques, such as FLASH radiotherapy, in which ultra-high dose rates (UHDR) are applied, have set a challenge in investigating whether the standard dosimetric systems used in conventional radiotherapy can still be used without further issues. In this context, it is necessary to understand how passive dosimeters, e.g., alanine based on electron paramagnetic resonance (EPR), respond to these UHDR conditions. Therefore, this study aimed to systematically analyse the use of alanine pellets under FLASH conditions. The pellets were irradiated with electron beams at 7 and 9 MeV from an ElectronFlash LINAC. The response was evaluated in terms of percentage depth dose (PDD) and as a function of dose per pulse (DPP). Experimental data are compared to Monte Carlo (MC) simulations and with a diamond detector as the reference detector. A good agreement between MC-simulated and experimental PDDs was found (variation <3 % for the 7 MeV beam). The alanine/EPR signal presented a linear response as a function of DDP, up to values of about 7 Gy/pulse, and no dose-rate dependence. In addition, average instantaneous dose rates were successfully estimated for different LINAC setups. These findings highlight the potential use of both MC simulations and alanine dosimeters in the planning and monitoring of delivered doses in the context of FLASH radiotherapy.