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 doserates>40 Gy s(-1), requires accurate real-time dosimetry.Approach.Silicon carbide(SiC)p-n diodedosimeters designed for the stringent requirements of FLASH radiotherapy have been fabricated andcharacterized in an ultra-high pulse dose rate electron beam. The circular SiC PiN diodes werefabricated at IMB-CNM(CSIC)in 3 mu m epitaxial 4H-SiC. Their characterization was performed inPTB's ultra-high pulse dose rate reference electron beam. The SiC diode was operated without externalbias voltage. The linearity of the diode response was investigated up to doses per pulse(DPP)of 11 Gyand pulse durations ranging from 3 to 0.5 mu s. Percentage depth dose measurements were performed inultra-high dose per pulse conditions. The effect of the total accumulated dose of 20 MeV electrons inthe SiC diode sensitivity was evaluated. The temperature dependence of the response of the SiC diodewas measured in the range 19 degrees C-38 degrees C. The temporal response of the diode was compared to thetime-resolved beam current during each electron beam pulse. A diamond prototype detector(flashDiamond)and Alanine measurements were used for reference dosimetry.Main results.The SiCdiode response was independent both of DPP and of pulse dose rate up to at least 11 Gy per pulse and4 MGy s(-1), respectively, with tolerable deviation for relative dosimetry(<3%). When measuring thepercentage depth dose under ultra-high dose rate conditions, the SiC diode performed comparablywell to the referenceflashDiamond. The sensitivity reduction after 100 kGy accumulated dose was<2%. The SiC diode was able to follow the temporal structure of the 20 MeV electron beam even forirregular pulse estructures. The measured temperature coefficient was(-0.079 +/- 0.005)%/degrees C.Significance.The results of this study demonstrate for thefirst time the suitability of silicon carbidediodes for relative dosimetry in ultra-high dose rate pulsed electron beams up to a DPP of 11 Gy perpulse