Osld and Micro-Diamond Performance Under Ultra-High Dose Rate Flash Radiation Therapy
Abstract
Purpose
To evaluate the uses of beryllium oxide optically stimulated luminescent dosimeters (OSLDs) and solid-state micro-diamond detectors as viable dosimetry tools for ultra-high dose rate electron FLASH treatments.
Methods
One hundred beryllium oxide OSLDs from RadPro were irradiated together with EBT-XD film in a 35 MeV electron beam from the High Intensity Gamma Source (HIGS) at Triangle Universities Nuclear Laboratory (TUNL). Irradiations ranged from 1-25 Gy with dose rates between 1-25 MGy/s. OSLDs were read out thirty minutes post irradiation, and EBT-XD film was scanned 24 hours post exposure. Dose measurements were made with a PTW micro-diamond detector incorporating a flashAdapter. The FLASH diamond detector was first evaluated at clinical dose rates (0-20 Gy) on a commissioned TrueBeam (16 MeV electrons), and then applied to HIGS dose rates from 1-5 MGy/s.
Results
OSLD measured FLASH doses in the range 1-25 Gy were found to be proportional to corresponding film doses. However, a 25% increase between EBT-XD measured doses and OSLD doses was observed for FLASH dose rates in the MGy/s range. Measurements made by the micro-diamond detector at clinical dose rates varied significantly at extreme FLASH dose rates.
Conclusion
When OSLDs and EBT-XD film are calibrated at clinical dose rates and then applied to extreme FLASH dose rates (MGy/s), a 25% discrepancy was observed. The source of the discrepancy is under investigation and may be OSLD under-response or EBT-XD over-response, or some combination thereof. Micro-diamond detectors did not prove useful at these dose rates in this specific geometry.