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Silicon Carbide (SiC) detectors are recently emerging as promising alternative detectors for many applications in radiation detection, including dosimetry for radiotherapy, thanks to the observed high radiation hardness, time and energy resolution and the very good signal to noise ratio. SiC is, indeed, a semiconductor composed by 50% of silicon and 50% of carbon characterized by a wide bandgap (3.26 eV) and high e-h pair production energy (7.8 eV) leading to a reduced leakage current and extremely interesting performances in radiation detection [1].
A collaboration involving the INFN Catania Division and the local start-up ST-Lab (Catania) has been established to develop PiN junction SiC detectors of different active thicknesses (0.2- 20 um thick) and areas (1-10 mm2) optimized for the dosimetry in conventional radiotherapy as well as for the emerging alternative radiotherapic techniques as the FLASH radiotherapy.
In particular, FLASH radiotherapy is a technique still under study which makes use of ultra-high dose-rate (UHDR) particle beams (> 40 Gy/s) for irradiating tumors thanks to the observed improved sparing (FLASH effect) of the healthy tissues as respect to the conventional radiotherapy which uses beams with dose rates of a few Gy/min. Due to the completely different temporal characteristics of the FLASH radiotherapy, all the dosimeters recommended for the conventional radiotherapy, as ionization chambers, suffer of not-negligible ion recombination effects which make them unusable with UHDR beams. For such reasons, a big effort is nowadays dedicated on identifying and developing alternative detectors still able to maintain the accuracy needed for radiotherapy. The mentioned SiC detectors were optimized for this purpose and have been already successfully tested with UHDR 9 MeV pulsed electron beams using the SIT Sordina ElectronFLASH accelerator available at the Centro Pisano for Flash Radio Therapy (CPFR) in Pisa, founded by the Fondazione Pisa [2,3]. Numerous experiments allowed us to demonstrate the linearity of the realized SiC detectors response in charge up to a dose per pulse of 21 Gy/pulse and instantaneous dose rate exceeding 5 MGy/s [2,3]. Moreover, single pulse shape time measurements at high time resolution (ns) were also performed by connecting the detectors to a fast oscilloscope and comparing the signals with the current transformer (ACCT) used as established monitoring system of the machine [4]. These measurements enabled to demonstrate the capability of also monitoring the possible variation of the intra-pulse instantaneous dose rate. In the perspective of the beam monitoring, a never explored configuration of the SiC detectors was also developed where the bulk thick substrate placed below the active layer in the standard structure, is removed through an electrochemical process to increase the transparency of the sensor and minimize the beam perturbation [2]. Moreover, following such excellent results, a more complex geometrical structure consisting of a linear array of multiple small size SiC detectors will be also developed within the framework of the INFN-CNTT financed R4I project “DREAM” recently started at INFN-CT, with the aim of measuring the spatial dose distribution of UHDR electron beams with high spatial resolution and with a reduced accumulated total dose. The results of the numerous experimental runs performed in the recent years will be reported in detail.
These developments have been performed within the framework of the INFN call “FRIDA” financed by the CSN5 and within the contest of the National Plan for NRRP
Complementary Investments (PNC0000003) project AdvaNced Technologies for Human centrEd Medicine (ANTHEM).
References
[1] De Napoli, M. SiC detectors: A review on the use of silicon carbide as radiation detection material. Front. Phys. 2022, 10, 898833.
[2] F. Romano et al., First Characterization of Novel Silicon Carbide Detectors with Ultra-High Dose Rate Electron Beams for FLASH Radiotherapy, Applied Sciences, 13(5), 2986.
[3] G. Milluzzo et al., Comprehensive dosimetric characterization 1 of novel Silicon Carbide detectors with UHDR electron beams for FLASH radiotherapy, in press in Medical Physics, DOI: 10.1002/mp.17172
[4] C. Okpuwe et al, Silicon carbide detectors for dosimetry and monitoring of ultra-high dose rate beams 2024 JINST 19 C03064
