Speaker
Description
Flash therapy is a radiation therapy technique that aims to take advantage of the potentially greater effectiveness of treatment using electrons with high absorbed dose rates, approximately 1 MGy/s. Several LINACs are currently being installed and tested to demonstrate the clinical benefits of this irradiation method. Laser acceleration processes promise even higher rates, about 100 GGy/s, obtained with pulses of a few fs. CEA LIST LNHB (French National Metrology Laboratory for Ionizing Radiation) has been tasked with establishing the traceability of these ultra-flash irradiations in terms of absorbed dose to water.
A 100 TW laser acceleration facility (UHI100) capable of producing electron beams of around 100 MeV with very short pulses (25 fs) with an absorbed dose per pulse of a few mGy is studied. A chemical transfer dosimeter calibrated in terms of absorbed dose to water in a 18 MeV electron beam delivering pulses of about 3.4 µs duration, has been chosen. This beam, established according to the specifications of IAEA Protocol 398 and 483, is traceable to its primary standard in terms of absorbed dose in water.
The transfer dosimeter is based on the chemical compound named resazurin that transforms into resorufin which is fluorescent, allowing a direct read by photoluminescent spectroscopy.
However, LNHB and ultra-high dose rate facilities are quite different. To account for the differences in terms of energy and duration of the pulses, correction factors, for radiation quality, and non-linearities for dose and dose rate, have to be applied to the calibration coefficient measured at LNHB.
This presentation will present those correction factors established through experimental results and Monte-Carlo calculations. Once corrected the transfer dosimeter is then used to calibrate the monitor of the Ultra-flash facility insuring the traceability of the irradiation against the national reference in terms of absorbed dose to water.