An innovative dose rate independent 2D Ce-doped YAG scintillating dosimetry system for time resolved beam monitoring in ultra-high dose rate electron FLASH radiation therapy

TL;DR

This paper introduces a novel 2D real-time dosimetry system for ultra-high dose rate electron FLASH radiation therapy, demonstrating dose linearity, independence from dose rate and energy, and pulse discrimination capabilities.

Contribution

The study presents an innovative, dose rate independent 2D dosimetry system using Ce-doped YAG scintillating material with high temporal resolution for FLASH-RT applications.

Findings

Linear dose response up to 13 Gy for doses > 3.5 Gy

No dose rate dependence up to 140 Gy/s and 300 Hz PRF

Capable of measuring individual pulse doses up to 250 Hz PRF

Abstract

FLASH-RT has proven beneficial in preclinical studies. However, the lack of accurate real time 2D dosimetry is a limiting factor. In this work, an innovative solution for 2D real time dosimetry in UHDR electron beams is presented. The in-house developed ImageDosis system consists of a scientific camera, with high temporal resolution, and a coating, containing 12% of Y$_3$Al$_5$O$_{12}$:Ce$^{3+}$ as scintillating material. Reference dosimetry was performed by means of radiochromic film, and a (C$_{38}$H$_{34}$P$_2$)MnBr$_4$ point scintillator was used to validate the pulse discrimination properties of the ImageDosis system. Irradiations were performed in two centers (Antwerp and Orsay), with an ElectronFlash accelerator, with varying number of pulses, pulse length, pulse repetition frequency (PRF) and energy. Also, the temporal resolution and 2D properties were investigated. For doses > 3.5 Gy, the ImageDosis showed a linear dose response up to at least 13 Gy. No dose rate dependence was found for an average dose rate up to 140 Gy/s, a dose per pulse up to 2 Gy and a PRF up to 300 Hz. The ImageDosis system showed capable of measuring the dose of the individual pulses up to a PRF of 250 Hz, but did not detect 3% of the pulses, because these pulses were delivered during the dead time of the camera. The maximal difference in FWHM of the field size between the ImageDosis system and the reference was 3.6%. For a nominal field size of 100 mm and 120 mm, a decreased output was observed on the superior part of the field. The ImageDosis system showed linear dose response and no dose rate nor energy dependence. It showed capable of discriminating and measuring the dose of individual pulses and promising 2D characteristics that need further optimization.