Characterization of silicon carbide diodes as cost-effective active detectors for proton UHDR dosimetry

Background

Proton therapy allows for better localization of the dose distribution in the tumor. In addition, the FLASH effect can be exploited to reduce the toxicity to healthy tissue by using short-pulsed treatment at ultra-high dose rates (UHDR). Such intense radiation conditions have limited options for active detectors for dosimetry.

Purpose

Silicon carbide-based diodes are proposed as a cost-effective alternative to diamond detectors for dosimetry in UHDR.

Methods

Two new SiC diodes designed and fabricated at the Institute of Microelectronics of Barcelona (IMB-CNM) were exposed to 20 $\mu s$ proton low-energy pulses with up to 25 Gy per pulse to verify the capability of this technology to function under UHDR radiation at the Center for Microanalysis of Materials (CMAM) facility. The response of a single diode was correlated to the dose per pulse measured with calibrated EBT4 radiochromic films. Likewise, a 2 $\times$ 2 dosimeter matrix mounted on a motorized stage system was used as a proof-of-concept for a large array dose monitor under construction, by scanning the response of each of its pixels as a function of position with respect to the beam, compared against calibrated radiochromic films. Finally, the same device was exposed to varying pulse lengths, while connected to a current-to-voltage amplifier and an oscilloscope in order to measure the pulse structure.

Results

First, the single diode showed a good dose rate linearity. No indication of saturation was observed even at the highest dose per pulse (DPP) of 25 Gy. This was observed even after over-exposure of 52 kGy of 7 MeV protons, although its response lowered to 31% of the initially measured value. Second, the beam profiles observed by the pixelated detector were consistent with those of the reference measurements. Finally, the full width half maximums of the pulses observed by the pixels show good correlation with the pulse width of the beam.

Conclusions

The SiC detectors developed at IMB-CNM were able to withstand and accurately measure the dose under FLASH compatible beam characteristics, even in the case of low-energy protons (7 MeV). The pixelated device showed promising results for a full array monitor for quality assurance, and the capability of time-resolved pulse measurements, the latter after optimization of the electronics.