Performance evaluation of a new type of commercial silicon detectors for photon beam dosimetry

Modern radiotherapy relies on advanced treatment techniques that utilize a large number of small fields, for which maintaining dosimetric accuracy is often challenging. Most vendors have introduced microdetectors suitable for small field dosimetry. Sun Nuclear has developed two silicon diodes with a sensitive volume of 0.35 mm³ that are intended to replace their current EDGE diode detector. Detector characterization is required before it can be used for clinical practices.

Two Sun Nuclear silicon detectors (unshielded model 1048 and shielded model 1049) are evaluated to characterize their relative dosimetric performance in megavoltage photon beams, with particular emphasis on small fields.

Sun Nuclear silicon detectors are identical in physical dimensions except that model 1049 is shielded. These detectors are investigated in Varian TrueBeam photon beams (6 MV, 6 MV FFF, 10 MV, 10 MV FFF and 15 MV) for dose linearity, dose rate linearity, thermal stability, and usability for small fields across multiple photon energies. The measured data are benchmarked against Monte Carlo (MC) simulation using EGSnrc for depth dose, profile and output factors. Additionally small field correction parameters $k_{Q_{clin},Q_{msr}}^{f_{clin},f_{msr}}$ were determined experimentally and compared to Monte Carlo data.

These detectors exhibited excellent dose linearity across five photon energies, with only a minor deviation of approximately 1.5% at doses below 2 MU. The dose rate linearity remained stable from 100 MU/Min to highest dose rate for all beam energies with a slight upward trend of 1.5% for lower dose rates. Both detectors are also temperature independent, within 1.0% over the range of 4°C-40°C. Depth dose and profiles measurements showed good agreement with Monte Carlo data across the applicable field size range. For small field dosimetry, shielded detector exhibited a pronounced signal reduction for fields smaller than 2 cm, resulting in large correction factors, whereas the unshielded detector demonstrated favorable and stable performance.

Both silicon diodes have excellent dosimetric characteristics, providing reproducible data with signal linearity. They also provide a large signal (nC). For smallfield photon dosimetry, the unshielded detector yielded superior performance across all investigated energies.