Orientation‑Dependent Performance of a Microsilicon Detector In Small‑Field Dosimetry
Abstract
Purpose
Accurate small‑field dosimetry is strongly influenced by detector volume averaging, density effects, and perturbations. Solid‑state detectors such as microSilicon and microdiamond are widely used due to minimal correction requirements; however, limited data exist on the impact of detector orientation and measurement depth. This study evaluates orientation‑dependent differences in field output factors (FOFs) and beam profiles for small photon fields.
Methods
A PTW microSilicon detector was evaluated in face‑up and edge‑on orientations on a TrueBeam linear accelerator. FOFs were measured for field sizes from 0.5×0.5cm² to 10×10cm² using 6 MV and 6 MV flattening‑filter‑free (FFF) beams at 100 cm source‑to‑axis distance and depths of dmax, 5 cm, and 10 cm in water. In‑plane and cross‑plane beam profiles were acquired using a water scanning system. Measured FOFs were compared between orientations and benchmarked against Monte Carlo (MC) simulations. Orientation‑dependent full width at half maximum (FWHM) and penumbra were analyzed to assess spatial resolution.
Results
Detector orientation produced clinically relevant differences for sub‑centimeter field sizes. For a 0.5×0.5 cm² field, the face‑up orientation underestimated FOFs by 5–6% relative to the edge‑on configuration. Orientation‑dependent differences decreased with increasing field size and were less than 0.5% for fields ≥1.5×1.5 cm². Compared with MC simulations, the edge‑on orientation showed closer agreement across all field sizes, remaining within 3% even for the smallest field. Profile analysis demonstrated superior spatial resolution in the edge‑on orientation. Face‑up measurements exhibited 3–10% FWHM narrowing and 6–11% penumbra underestimation, with increasing effects for smaller fields and greater depths.
Conclusion
The edge‑on orientation is preferred for microSilicon detectors in small‑field dosimetry, providing improved agreement with Monte Carlo simulations and more accurate beam profile characterization. The face‑up orientation may be acceptable for fields ≥1×1 cm² but introduces systematic underestimation in sub‑centimeter fields, underscoring the need for orientation‑specific standardization in small‑field reference measurements.