Session Item

In FLASH radiation therapy, the ability to monitor the beam output and measure the physical beam parameters are not a trivial task due to extremely high dose-rate and dose-per-pulse (DPP) conditions. In this study, we are characterizing the response of a water-equivalent detector that provides real-time dose measurements: the W2 Exradin Scintillator (Standard Imaging. Inc).  

The W2 Exradin plastic scintillator detector (PSD) was exposed to different parameters relevant to FLASH by modifying the pulse repetition frequency (PRF), pulse width (PW), and pulse amplitude settings for an IntraOp electron FLASH Mobetron accelerator. The response of the W2 Exradin PSD was evaluated as a function of dose, DPP, and mean and instantaneous dose-rate using the blue and green signal channels as well as the net signal from subtracting the green signal from the blue. To account and correct for any detector radiation damage, the Cherenkov Light Ratio (CLR) for the W2 Exradin PSD was measured and tracked as a function of dose history.

The response of the W2 Exradin PSD was found to be linear and independent of mean dose-rate at a DPP setting of 0.5 Gy. At higher DPP settings, the W2 demonstrated nonlinear behavior and saturation in signal at higher doses and PRFs. The measured signal in the blue and green channel at each dose per pulse was found to be linear up to a threshold DPP of 1.2 Gy/pulse. In evaluating instantaneous dose-rate dependence, the measured signal was found to be saturating at higher pulse width values when matching the DPP (up to 10-20% under response for the net signal at higher pulse widths).  

In this study, we have shown that in its current configuration the W2 PSD as a feasible detector that can provide real-time dose measurements under a certain range of FLASH conditions given that radiation damage and DPP are properly accounted for.  These findings will inform on future design modifications to improve their performance in FLASH beamlines.