State-of-the-art silicon carbide diode dosimeters for ultra-high dose-per-pulse radiation at FLASH radiotherapy.

OBJECTIVE: The successful implementation of FLASH radiotherapy in clinical settings, with typical dose rates >40Gy/s, requires accurate real-time dosimetry.

APPROACH: Silicon carbide p-n diode dosimeters designed for the stringent requirements of FLASH radiotherapy have been fabricated and characterized in an ultra-high pulse dose rate electron beam. The circular SiC PiN diodes were fabricated at IMB-CNM (CSIC) in 3μm epitaxial 4H-SiC. Their characterization was performed in PTB's ultra-high pulse dose rate reference electron beam. The SiC diode was operated without external bias voltage. The linearity of the diode response was investigated up to doses per pulse of 11Gy and pulse durations from 3 to 0.5μs. Percentage depth dose measurements were performed in ultra-high dose per pulse conditions. The effect of the accumulated dose of 20MeV electrons in the SiC diode sensitivity was evaluated. The temperature dependence of the response of the SiC diode was measured in the range 19-38°C. The temporal response of the diode was compared to the time-resolved beam current during each electron beam pulse. A flashDiamond prototype detector and Alanine measurements were used for reference dosimetry.

MAIN RESULTS: The SiC diode response was independent both of DPP and of pulse dose rate up to at least 11Gy per pulse and 4MGy/s with tolerable deviation for relative dosimetry (<3 %). When measuring the percentage depth dose under UHDR conditions, the SiC diode performed comparably well to the reference flashDiamond. The sensitivity reduction after 100kGy accumulated dose was <2%. The diode was able to follow the temporal structure of the 20 MeV electron beam even for irregular pulse estructures. The measured temperature coefficient was (-0.079±0.005)%/ºC.

SIGNIFICANCE: The results of this study demonstrate for the first time the suitability of silicon carbide diodes for relative dosimetry in ultra-high dose rate pulsed electron beams up to a DPP of 11Gy per pulse.&#xD.