Clinical application of an unshielded silicon diode detector for relative electron beam dosimetry

Relative electron beam dosimetry requires careful consideration of detector-specific effects, including material dependent stopping-power ratios, effective point of measurement, and volume averaging. Ionization chambers require percentage depth ionization (PDI) to percentage depth dose (PDD) conversion, while suitable silicon diode detectors may directly measure absorbed dose due to their more water-equivalent stopping-power behavior.

This study aims to evaluate the unshielded silicon diode detector SunSILICON 1048 (Sun Nuclear) for clinical electron beam dosimetry by assessing its suitability for measurement of PDDs, lateral beam profiles, and output factors.

Comparative measurements between SunSILICON and different types of ionization chambers (SNC350p, SNC125c, SNC600c, all Sun Nuclear Corp.), as well as PTW's silicon diode detector microSilicon were taken on a Varian TrueBeam linear accelerator using a SunSCAN 3D water phantom for electron beam energies from 6 MeV to 22 MeV and field sizes from 6 cm × 6 to 25 cm × 25 cm. Ion chamber PDIs were converted to PDDs; silicon detector PDIs were evaluated directly. The agreement between repeated measurements conducted with different detectors was assessed using 1D gamma criteria.

SunSILICON PDDs agreed with SNC350p derived PDDs within ± 1% for all energies except in the 6 MeV buildup region. Gamma passing rates exceeded 94.5% except for 6 MeV, where deviations were confined to the buildup region. Lateral profiles showed gamma passing rates exceeding 96.7%, with differences dominated by ion chamber volume averaging. Comparisons with microSilicon exceeded 99% agreement for both PDDs and lateral profiles. Output factors matched SNC600c within 0.85% RMS.

SunSILICON provides accurate, direct measurements of PDDs, lateral beam profiles, and output factors. Its water-equivalent design minimizes perturbation and gradient related errors, confirming its suitability for clinical electron beam dosimetry.