| Metadata | Details |
|---|
| Publication Date | 2023-02-25 |
| Journal | Applied Sciences |
| Authors | F. RomanĂČ, G. Milluzzo, Fabio Di Martino, Maria Cristina DâOca, G. Felici |
| Institutions | Institute for Microelectronics and Microsystems, Belgian Nuclear Research Centre |
| Citations | 32 |
| Analysis | Full AI Review Included |
- Core Value Proposition: Novel Silicon Carbide (SiC) PIN junction detectors were successfully characterized for use in Ultra-High Dose Rate (UHDR) electron beam dosimetry, specifically for FLASH radiotherapy.
- Performance Advantage: SiC offers a superior compromise between the maturity of Silicon technology and the extreme robustness of diamond, featuring a high bandgap (3.23 eV) and high radiation hardness (30-40 eV displacement energy).
- Linearity Achievement: The 10 ”m thick SiC sensor demonstrated a linear charge response as a function of dose-per-pulse (D/p) up to 2 Gy/pulse, significantly exceeding the performance of a reference Silicon diode (saturation observed around 0.5 Gy/pulse).
- Radiation Hardness: The detector exhibited excellent stability, maintaining charge per pulse measurements within ±0.75% variability after accumulating a total dose of 90 kGy.
- Experimental Setup: Characterization utilized 9 MeV electron beams generated by the dedicated SIT Sordina ElectronFLASH LINAC, with a fixed pulse duration of 2 ”s.
- Future Development: Simulations confirm that ultrathin, free-standing SiC membranes (substrate removed) are critical for in-transmission beam monitoring, minimizing angular scattering and energy degradation of the incident beam.
| Parameter | Value | Unit | Context |
|---|
| Detector Type | PIN Junction | N/A | SiC sensor structure |
| SiC Polytype | 4H-SiC | N/A | Material used |
| Active Area | 1 x 1 | cm2 | Sensor geometry tested |
| Active Layer Thickness | 10 | ”m | Thickness of the low-doped n- layer |
| Substrate Thickness | 370 | ”m | n+ thick substrate (removed for free-standing membrane) |
| Operational Voltage | 480 | V | Applied reverse bias (ensuring full depletion) |
| Electron Beam Energy | 9 | MeV | Nominal energy used for characterization |
| Pulse Duration | 2 | ”s | Fixed duration for all measurements |
| Linear Response Range | Up to 2 | Gy/pulse | Dose rate linearity limit (limited by electrometer peak current) |
| Cumulative Dose Tested | 90 | kGy | Total accumulated dose for radiation hardness test |
| Charge Stability (90 kGy) | ±0.75 | % | Variation in charge per pulse over cumulative dose |
| SiC Energy Gap (Eg) | 3.23 | eV | Material property |
| e-h Pair Creation Energy | 7.6-8.4 | eV | Determines sensitivity (lower than Diamondâs 13 eV) |
| Displacement Energy | 30-40 | eV | High radiation resistance (compared to Si: 13-15 eV) |
| SiC Density | 3.22 | g/cm3 | Material property |
- Detector Biasing and Readout: The SiC sensor was operated at 480 V reverse bias. Charge collection and voltage supply were managed using a Keithley 6517A electrometer, connected via a BNC cable.
- Beam Generation: A SIT Sordina ElectronFLASH LINAC was used, providing 9 MeV electron beams with a fixed pulse duration of 2 ”s, operating in FLASH mode.
- Dose-per-Pulse (D/p) Variation: Different D/p values (ranging from 0.21 Gy/p to 5.27 Gy/p) were achieved by varying the diameter of PMMA cylindrical applicators (3.5 cm to 12 cm) and adjusting the Applicator-to-Detector Distance (ADD).
- Reference Dosimetry: The absorbed dose was independently measured using two standard passive dosimeters placed at the same position as the SiC detector:
- Alanine pellets (dose extracted via Electron Paramagnetic Resonance, EPR).
- EBT-XD radiochromic films (scanned and analyzed using FilmQA Pro software).
- Dose Uniformity Check: RCF-EBT3 films were used to verify dose uniformity over the 1 x 1 cm2 active area of the SiC detector, confirming flat profiles over a 15 mm length.
- Radiation Hardness Testing: The detector was repeatedly irradiated (400 pulses at 5 Gy/pulse, 5 Hz) up to 90 kGy cumulative dose. Leakage current and charge per pulse were monitored after each irradiation sequence to assess degradation.
- Monte Carlo Simulation: Geant4 toolkit was employed to model energy deposition in SiC layers of varying thicknesses (2 ”m to 20 ”m) and to simulate the effect of the 370 ”m bulk substrate on the angular distribution of the 9 MeV electron beam.
- FLASH Radiotherapy (FLASH-RT): Primary application for real-time, active dosimetry and beam monitoring in UHDR electron LINACs, addressing the critical challenge of ion recombination in conventional ionization chambers.
- Clinical Quality Assurance (QA): Use as a robust, high-stability detector for daily QA checks of UHDR accelerators, ensuring consistent dose delivery and beam characteristics.
- High-Flux Beam Monitoring: Applicable in research and industrial settings involving high-intensity pulsed electron or proton beams (e.g., IORT systems, high-energy physics experiments) where radiation hardness is paramount.
- In-Transmission Dosimetry: The proposed ultrathin, free-standing SiC membrane configuration is ideal for monitoring the beam profile and intensity during treatment without significantly perturbing the beam path (low angular scattering).
- Radiation Hard Electronics: SiCâs high displacement energy and wide bandgap make it suitable for sensor and electronic components operating in extreme radiation environments (e.g., space, nuclear reactors).
View Original Abstract
Ultra-high dose rate (UHDR) beams for FLASH radiotherapy present significant dosimetric challenges. Although novel approaches for decreasing or correcting ion recombination in ionization chambers are being proposed, applicability of ionimetric dosimetry to UHDR beams is still under investigation. Solid-state sensors have been recently investigated as a valuable alternative for real-time measurements, especially for relative dosimetry and beam monitoring. Among them, Silicon Carbide (SiC) represents a very promising candidate, compromising between the maturity of Silicon and the robustness of diamond. Its features allow for large area sensors and high electric fields, required to avoid ion recombination in UHDR beams. In this study, we present simulations and experimental measurements with the low energy UHDR electron beams accelerated with the ElectronFLASH machine developed by the SIT Sordina company (IT). The response of a newly developed 1 à 1 cm2 SiC sensor in charge as a function of the dose-per-pulse and its radiation hardness up to a total delivered dose of 90 kGy, was investigated during a dedicated experimental campaign, which is, to our knowledge, the first characterization ever done of SiC with UHDR-pulsed beams accelerated by a dedicated ElectronFLASH LINAC. Results are encouraging and show a linear response of the SiC detector up to 2 Gy/pulse and a variation in the charge per pulse measured for a cumulative delivered dose of 90 kGy, within ±0.75%.
- 2017 - Faster and safer? FLASH ultra-high dose rate in radiotherapy [Crossref]
- 2019 - Clinical translation of FLASH radiotherapy: Why and how? [Crossref]
- 2019 - Re: Differential impact of FLASH versus conventional dose rate irradiation: Spitz et al [Crossref]
- 2017 - Experimental platform for ultra-high dose rate FLASH irradiation of small animals using a clinical linear accelerator [Crossref]
- 2014 - Ultrahigh dose-rate FLASH irradiation increases the differential response between normal and tumor tissue in mice [Crossref]
- 2018 - X-rays can trigger the FLASH effect: Ultra-high dose-rate synchrotron light source prevents normal brain injury after whole brain irradiation in mice [Crossref]
- 2018 - Experimental set-up for FLASH proton irradiation of small animals using a clinical system [Crossref]
- 2019 - Feasibility of proton FLASH effect tested by zebrafish embryo irradiation [Crossref]
- 2022 - Ultra-high dose rate dosimetry: Challenges and opportunities for FLASH radiation therapy [Crossref]
- 2020 - Beam monitors for tomorrow: The challenges of electron and photon FLASH RT [Crossref]