Evaluation of the Sun Nuclear Sunsilicon Diode for Small-Field Dosimetry In 1.5 T and 0.35 T MR-Linacs
Abstract
Purpose
Accurate small‑field dosimetry on MR‑linacs remains challenging due to magnetic‑field–induced dose perturbations and steep dose gradients. In this study, the performance of a newly developed unshielded silicon diode has been evaluated for use in small-field dosimetry with MR-linacs, and benchmarks the findings against more established commercial detectors on 1.5T and 0.35T MR-linac platforms.
Methods
Output factors were measured on Elekta Unity (1.5T) and ViewRay MRIdian (0.35T) MR-linacs with the Sun Nuclear SunSILICON (1048) and PTW microDiamond (60019). For the Elekta Unity, beam profiles were also acquired, and a Standard Imaging Exradin W2 was used as an additional detector for comparison. At 1.5T, outputs for square fields ranging from 0.5×0.5 to 10×10 cm² were acquired and normalized to 10×10 cm². Crossline profiles were used to peak-scale central-axis output factors. At 0.35T, fields from 9.96×9.96 to 0.83×0.83 cm² were measured and normalized to 9.96×9.96 cm². Detector alignment was verified via crossline and inline couch translations. Output factors were corrected using published TRS-483 and TRS-483 corrections.
Results
At 1.5T, TRS-483-corrected SunSILICON output factors agreed with the microDiamond within 0.6% for fields ≥2×2 cm² and within 2.0% for smaller fields. The largest differences occurred at 0.5×0.5 cm², where SunSILICON differed from microDiamond by 1.8% and from W2 by 2.6%. Inline and crossline profiles at 1.5T were consistent across detectors, with full width at half max values agreeing within 0.05 cm. At 0.35T, SunSILICON and microDiamond output factors agreed within 0.7% for all measured fields.
Conclusion
This work provides cross-platform evidence on the performance of an unshielded silicon diode for small-field output-factor measurements in the presence of magnetic fields. Corrected output-factors were comparable to reference detectors with differences increasing for the smallest fields at 1.5T. This data can be used when considering diode measurements for MR-linac commissioning and routine QA.