Characterization of two new unshielded and shielded silicon diode detectors for external beam radiation therapy: SunSILICON and SunSILICON P

• Linearity and Reproducibility: The new silicon diode showed a good linear response within 0.2 % for dose values ranging from 0.02 Gy to 36 Gy with deviations as low as 0.07 %. • Dose Rate Dependence: The new silicon diode maintained a dose rate dependence below 1 %, even for heavily pre-conditioned detectors. The response ratio remained stable within ±0.1 % across various pulse frequencies. • Temporal Response: The new silicon diode has a near-instantaneous response to radiation. The detectors exhibited minimal post-irradiation leakage current, even at high accumulated dose levels. • Signal-to-Noise Ratio: The signal noise of the SunSILICON and SunSILICON P detectors was below 0.73 %. • Temperature Dependence: The temperature dependence of the response was minimal at 0.06 %/K. • Accumulated Dose Dependence: The accumulated dose dependence of the new silicon diode was tested for different beam energies and beam qualities: It was very low with less than 0.1 %/kGy for 6 MV photons, less than 0.5 %/kGy for 15 MV photons, and less than 1.5 %/kGy for 20 MeV electrons. • Impedance and Leakage: The diode’s impedance and leakage characteristics were stable, with an average impedance of 4.4 GΩ at 20 °C and a comparably low leakage current of 2.6 pA at an input offset voltage of 10 mV. Radiation dosimeters are essential for measuring beam characteristics in external beam radiotherapy. While ionization chambers are widely used, they have limitations such as large active volumes or small signal strengths. Silicon diodes, with their high density and low mean energy required to generate electron-hole pairs, offer superior spatial resolution and sensitivity. This study aims to evaluate the characteristics of a newly developed silicon diode embedded in SunSILICON and SunSILICON P for relative dosimetry in external beam radiotherapy. The evaluation involved fundamental tests such as reproducibility, linearity with dose, and speed of response. Critical aspects like impedance and leakage characteristics, accumulated dose dependency, temperature dependency, pulse repetition frequency dependence, and instantaneous dose rate dependency were also assessed. Measurements were performed using a Varian TrueBeam clinical linear accelerator and 60 Co, with most tests conducted in water equivalent HE Solid Water slab phantoms. The SunSILICON and SunSILICON P detectors demonstrated a linear response, and the dose rate dependence of the response was below 1 %, even for pre-conditioned detectors. The detectors showed a near-instantaneous response to radiation. The diode features a high signal-to-noise ratio and low leakage. The temperature dependence of the response was 0.06 %/K, and the accumulated dose dependence was less than 0.1 %/kGy for 6 MV photons. The SunSILICON and SunSILICON P detectors exhibit excellent characteristics for clinical use in external beam radiation therapy. Their high sensitivity, low noise, and minimal dose rate and temperature dependencies make them reliable tools for accurate dosimetry. These results provide a foundation for further clinical evaluation and validation of these detectors.