Characterization of a Diode Dosimeter for UHDR FLASH Radiotherapy

TL;DR

This study characterizes a diode-based detector for ultra-high dose rate FLASH radiotherapy, demonstrating its accuracy, linearity, and temporal resolution in measuring dose, dose rate, and dose per pulse in UHDR electron beams.

Contribution

The paper introduces a newly designed diode EDGE Detector with an electrometer, validated for accurate dosimetry in UHDR FLASH radiotherapy, showing improved temporal and dose measurement capabilities.

Findings

The EDGE Detector agrees with film measurements within 2% for dose up to 70 Gy.

It maintains dose linearity and dose rate independence in UHDR beams.

The detector can resolve dose and dose rate at sub-millisecond timescales.

Abstract

Purpose: A diode EDGE Detector with a newly designed electrometer has been characterized for use in an UHDR electron beam and demonstrated appropriateness for UHDR FLASH radiotherapy dosimetry. Methods: Dose linearity, mean dose rate, and dose per pulse dependencies of the EDGE Detector were quantified and compared with dosimeters including a W1 scintillator detector, radiochromic film, and ionization chamber that were irradiated with a 10 MeV UHDR beam. The dose, dose rate and dose per pulse were controlled via an in-house developed scintillation-based feedback mechanism, repetition rate of the linear accelerator, and source-to-surface distance, respectively. Depth-dose profiles and temporal profiles at individual pulse resolution were compared to the film and scintillation measurements, respectively. The radiation-induced change in response sensitivity was quantified via irradiation of ~5kGy. Results: The EDGE Detector agreed with film measurements in the measured range with varying dose (up to 70 Gy), dose rate (nearly 200 Gy/s), and dose per pulse (up to 0.63 Gy/pulse) on average to within 2%, 5%, and 1%, respectively. The detector also agreed with W1 scintillation detector on average to within 2% for dose per pulse (up to 0.78 Gy/pulse). The EDGE Detector signal was proportional to ion chamber (IC) measured dose, and mean dose rate in the bremsstrahlung tail to within 0.4% and 0.2% respectively. The EDGE Detector measured percent depth dose agreed with film to within 3% and per pulse output agreed with W1 scintillator to within -6% to +5%. Conclusions: The EDGE Detector demonstrated dose linearity, mean dose rate independence, and dose per pulse independence for UHDR electron beams. It can quantify the beam spatially, and temporally at sub millisecond resolution.