Speaker
Description
The main challenge in radiotherapy (RT) is to deliver a sufficiently high curative dose to the tumour while maintaining tolerable doses to nearby organs at risk, and new treatment modalities are rapidly emerging. FLASH radiotherapy delivers a therapeutic dose several orders of magnitude faster (≥ 40 Gy/s) than conventional RT (0.05 Gy/s) and has been shown to reduce the likelihood of complications in normal tissues while providing a similar or better tumour control rate than conventional dose rates, reducing treatment time and organ motion-related issues. However, there are significant challenges to the clinical implementation of FLASH RT, as its requirements make most existing dosimetry equipment obsolete.
The physical properties of silicon carbide (SiC) make it an interesting material for radiation dosimetry. The wide bandgap of SiC reduces the rate of thermally generated charge carriers, thereby reducing leakage current and noise compared to silicon. Of particular interest is the signal yield per deposited mGy in SiC (425 pC/(mGy·mm3) for 4H-SiC) which is lower than for silicon. This makes SiC a good option for dosimetry in ultra-high dose pulsed radiation fields or direct beam monitoring, where the instantaneous dose deposition in the semiconductor is large and could saturate conventional silicon diodes. In addition, SiC has a higher displacement energy threshold and therefore higher radiation hardness than silicon. Today, SiC technology is mature and high quality substrates are available up to 200mm, allowing widespread use.
In this talk we will present the novel silicon carbide PiN diodes that have been designed and fabricated at IMB-CNM with the aim to respond to the technological challenges of FLASH RT. In a first characterization with 20 MeV FLASH electron beams at PTB (Germany), these diodes showed their suitability for relative dosimetry up to a dose of 11 Gy per pulse (4 MGy/s) and a dosimetric performance comparable to commercial diamond dosimeters [doi:10.1088/1361-6560/ad37eb]. The performance of the SiC diodes with FLASH proton beams was tested with 7 MeV protons at CMAM (Spain) where they showed good signal linearity with dose rate and reproducible response up to a dose per pulse of at least 20 Gy. Finally, the radiation resistance of the diodes was studied at CNA (Spain) using high LET, intense pulsed proton beams. The sensitivity of the diodes showed a progressive decrease at an initial rate of -1.34%/kGy of 1 MeV protons, and stabilised only for doses close to 750 kGy. However, the linear response with dose per pulse was maintained over a wide range of dose rates even for cumulative doses of several MGy. All of these measurements were made without the need for an external applied voltage. In conclusion, silicon carbide diodes fabricated at IMB-CNM are a real alternative to silicon and diamond dosimeters in a wide range of applications where accurate real-time relative dosimetry, fast response and long-term stability are required.
