Performance Comparison of a Plastic Scintillation Detector and Various Detectors for Small Field Dosimetry In High-Aspect-Ratio Rectangular Fields
Abstract
Purpose
Jaw geometry in elongated fields substantially impacts output factors (OPFs); therefore, reliance on square-field data alone cannot account for the physical effects. This study evaluated the response characteristics of various small-volume detectors in high-aspect-ratio small rectangular fields using a near-perturbation-free plastic scintillation detector (PSD) as a reference.
Methods
Experimental OPFs were measured for rectangular fields generated by fixing one jaw setting (from 1–4 cm) while varying the orthogonal jaw setting from 1 to 40 cm. Measurements were performed on a Varian TrueBeam Edge linac with 6-MV and 10-MV flattening filter-free beams using the following detectors: Medscint’s HYPERSCINT RP-200 PSD, PTW 60023 microSilicon diode, PTW 60019 microDiamond, PTW 31022 PinPoint 3D chamber, and PTW 31021 Semiflex 3D chamber. All OPFs were normalized to a 4 × 4 cm2 field, and detector-specific deviations relative to HYPERSCINT PSD were assessed. The influence of the detector orientation (stem effect) was evaluated for the chambers.
Results
The microSilicon diode demonstrated the closest agreement with the HYPERSCINT. The largest discrepancies were −1.1% for the microSilicon diode (2 × 1.5 cm2, 6-MV), +3.6% for the microDiamond (1 × 1 cm2, 10-MV), −3.8% for the PinPoint 3D chamber (1 × 1 cm2, 6-MV), and −8.0% for the Semiflex 3D chamber (1 × 1 cm2, 6-MV). For field sizes larger than 2 × 2 cm2, the OPF differences remained within 1.1% for all the detectors at both energies. The detector orientation dependence on the measured OPFs was notable; the PinPoint 3D chamber showed variations of up to 1.3% (1 × 20 cm2, 10-MV), whereas the Semiflex 3D chamber exhibited minimal variation (~0.2%).
Conclusion
The microSilicon diode showed the highest agreement with the HYPERSCINT PSD across rectangular fields ranging from 1 to 40 cm, signifying its suitability for accurate dosimetry in highly elongated fields.