Background and Aims

Background: Ultra-high dose rate (UHDR) FLASH beams typically deliver mean dose rates of >40Gy/sec. Characterization of these beams requires dosimeters which exhibit high spatiotemporal resolution and fast readout capabilities.

Aims: A diode EDGE Detector with a newly designed electrometer has been characterized for use in an electron beam and demonstrated appropriateness for FLASH radiotherapy dosimetry.

Methods

Methods: Dose linearity, mean dose rate, and dose-per-pulse dependencies of the EDGE Detector were quantified via irradiation with a 10 MeV UHDR electron beam. Parameters were controlled via an in-house developed scintillation-based feedback mechanism, repetition rate of the linear accelerator, and source-to-surface distance, respectively. Diode response was compared with dosimeters including a W1 scintillator detector, radiochromic film, and ionization chamber (IC). The radiation-induced change in response sensitivity was quantified via irradiation of ~5kGy. Depth-dose profiles and temporal profiles at individual pulse resolution were compared to the film and scintillation measurements, respectively.

Results

Results: The EDGE Detector agreed with film measurements in the measured range with varying dose (up to 70Gy), dose rate (nearly 200Gy/s), and dose-per-pulse (up to 0.63Gy/pulse, or 1.58x10^5Gy/s instantaneous dose rate for 4 microsecond pulses) on average to within 2%, 5%, and 1%, respectively. The EDGE Detector signal was proportional to IC measured dose, and mean dose rate in the bremsstrahlung tail to within 0.4% and 0.2% respectively. The radiation-induced response decrease was 0.4% per kGy. The EDGE Detector measured percent depth dose agreed with film to within 3% and per-pulse output agreed with W1 scintillator to within 4%.

Conclusions

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. It’s robustness and individual pulse detectability of treatment deliveries can potentially lead to its implementation for in vivo FLASH dosimetry, and dose monitoring.