Author: Petr Bruza, David J. Gladstone, Austin Sloop, Rongxiao Zhang 👨🔬
Affiliation: Thayer School of Engineering, Dartmouth College, Dartmouth Health 🌍
Purpose: UHDR-specific probes are becoming available on the market but often demand high costs and long order times. The reduced sensitivity of these probes often imposes challenges when measuring conventional beams. An electrometer that can rapidly and accurately measure the large impulses produced by standard solid-state probes under UHDR fluences is valuable for sites looking to expand their dosimetry toolbox. Per-pulse dosimetry from such a device expands the resources available for beam characterization, and of in-vivo verifications of dose rates and total delivered dose.
Methods: An IBA DoseX electrometer measured the signal from IBA Razor Diode and PTW UHDR-Microdiamond under UHDR conditions with a 90Hz pulse frequency. Measurements were compared to a validated UHDR electrometer designed around the EDGE diode and the Beam Current Transformers (BCT) installed in an IntraOp Mobetron irradiator. Doses were varied by modulating the pulse width and measurement geometry. Per-pulse measurements from the DoseX were obtained by characterizing the exponential decay of charge at the sampling circuits. Iterative fits isolate and eliminate the pulse pile-up seen in the base signal. Results focus on UHDR capabilities.
Results:
Integral measurements from the Razor diode agreed with other devices to less than 1% for conditions up to 4 Gy/pulse. Higher impulses up to 8Gy/pulse produced an over-response, averaging about 0.5% per additional Gy/pulse. Residual in the per-pulse reconstruction was ±1% up to 4Gy. Microdiamond integral measurements agreed to nearly 1% for 0.9 to 9 Gy/pulses.
Conclusion:
This version of DoseX is capable of recording integral and per-pulse UHDR dosimetry using standard clinical probes. Consistent behavior across such a wide dynamic range and differing probes aids the ability to measure in-vivo data in comparative FLASH studies. The accuracy of per-pulse dosimetry is adequate for information essential to commissioning and delivery verification for both experimental and trial in-vivo measurements.