Performance Evaluation of the New Commercial Exradin A30 Ion Chamber for Uhdr Reference Dosimetry
Abstract
Purpose
Ionization chambers represent the gold standard for clinical dosimetry; however, they suffer from severe ion recombination losses at the ultra-high dose rates (UHDR) characteristic of FLASH radiotherapy. This study evaluates the new commercial Exradin A30 parallel-plate ion chamber, optimized for UHDR reference dosimetry, paired with a modified electrometer capable of temporally resolved charge readouts.
Methods
The A30 parallel plate ionization chamber coupled to a modified Max Elite Electrometer was characterized using a 7 MeV UHDR electron beam produced by an Oriatron eRT. The A30 was positioned at dmax in a solid water phantom, 50 cm from the exit window. Radiation pulses were delivered at varying pulse widths (PWs) and electron gun currents to evaluate charge collection efficiency (CCE) across a range of doses per pulse (DPP, 0.07 – 12.1 Gy/pulse) and instantaneous (intra-pulse) dose rates (IDR) from 0.01 MGy/s (conventional dose rates) to 3 MGy/s at a fixed 4 µs PW. The chamber response was evaluated against Gafchromic film and a beam current transformer (BCT) placed at the beam exit window of the Oriatron to correct for machine output variations between deliveries.
Results
Collection efficiency decreased linearly with increasing IDR reaching a 5% loss (95% CCE) at approximately 0.5 MGy/s. The ion chamber response demonstrated excellent linearity (R2 > 0.9993) with respect to PW. Agreement between film and ion chamber dose measurements was within 5% for integrated film doses between 3.8 and 20.9 Gy.
Conclusion
The new commercial Exradin A30 parallel plate chamber, when paired with the Max Elite electrometer, provides a linear and accurate solution for UHDR reference dosimetry up to 0.5 MGy/s IDRs.