Moderator of 2 Sessions
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Presenter of 1 Presentation
DOSIMETRIC AND BIOLOGIC INTERCOMPARISON OF ELECTRON AND PROTON FLASH.
Abstract
Background and Aims
The FLASH effect has been validated in preclinical experiments with electrons (e-FLASH) and protons (p-FLASH) operating at a mean dose rate above 40 Gy/s. However, no systematic comparison of the FLASH effect produced by e- vs p-FLASH has been performed and constituted the aim of the present study.
Methods
The electron eRT6/Oriatron/CHUV/5 MeV and proton beam Gantry1/PSI/170 MeV were used to deliver conventional (0.1 Gy/s e-CONV and p-CONV) and UHDR (>100 Gy/s e-FLASH and p-FLASH). Protons were delivered in transmission. Dosimetry was performed with a system validated for e-FLASH beams and composed of alanine, TLD and gafchromic films (Jorge, 22). The FLASH effect was investigated using validated in vivo normal brain/GBM models in C57Bl6 mice. Neurocognitive sparing was evaluated 2/6 months post-WBI at 10 Gy and anti-tumor effect on GL261 subcutaneous tumors after local irradiation at 20 Gy with a follow-up > 3 months post-RT. The exact same geometry (17mm applicator) and experimental conditions were used in both sites.
Results
Doses measured at eRT6/Oriatron and at Gantry 1 were in agreement (± 2%) with reference dosimeters calibrated at CHUV/IRA.The neurocognitive capacity of e-/p-FLASH irradiated mice were indistinguishable from the controls whereas the e-/p-CONV showed irreversible cognitive decrements. Complete tumor response was obtained and similar between e-/p-FLASH vs e-/p-CONV.
Conclusions
Despite major structural differences between electron and proton beams, this study shows that dosimetric standards can be established. More importantly, the e-/p-FLASH effect (for neuro-toxicity and GBM response) is similar, suggesting that the most important physical parameter is the overall time of exposure in the range of the milliseconds, at least when small volumes are irradiated. It also suggests that the definition of a common profile will likely identify the molecular determinant of the FLASH effect.