Optically stimulated luminescence system as an alternative for radiochromic film for 2D reference dosimetry in UHDR electron beams.

Radiotherapy is part of the treatment of over 50% of cancer patients. Its efficacy is limited by the radiotoxicity to the healthy tissue. FLASH-RT is based on the biological effect that ultra-high dose rates (UHDR) and very short treatment times strongly reduce normal tissue toxicity, while preserving the anti-tumoral effect. Despite many positive preclinical results, the translation of FLASH-RT to the clinic is hampered by the lack of accurate dosimetry for UHDR beams. To date radiochromic film is commonly used for dose assessment but has the drawback of lengthy and cumbersome read out procedures. In this work, we investigate the equivalence of a 2D OSL system to radiochromic film dosimetry in terms of dose rate independency. The comparison of both systems was done using the ElectronFlash linac. We investigated the dose rate dependence by variation of the (1) modality, (2) pulse repetition frequency, (3) pulse length and (4) source to surface distance. Additionally, we compared the 2D characteristics by field size measurements. The OSL calibration showed transferable between conventional and UHDR modality. Both systems are equally independent of average dose rate, pulse length and instantaneous dose rate. The OSL system showed equivalent in field size determination within 3 sigma. We show the promising nature of the 2D OSL system to serve as alternative for radiochromic film in UHDR electron beams. However, more in depth characterization is needed to assess its full potential.