Evaluation of Plastic Scintillation Detectors for Quality Assurance In Non-Coplanar Stereotactic Radiotherapy
Abstract
Purpose
Non-coplanar arc irradiation is widely used in stereotactic radiotherapy to achieve highly conformal dose distributions for small targets. For patient-specific quality assurance (PSQA), detector performance must remain stable under continuous gantry rotation and varying couch angles. This study evaluated the suitability of a plastic scintillation detector (PSD) system for PSQA under clinically relevant non-coplanar stereotactic irradiation conditions.
Methods
QA measurements were performed using PSQA-like verification plans with a PSD system (Model 10, Blue Physics) and a PinPoint ionization chamber (PTW 31016) as a reference. A fixed square field size of 2 by 2 centimeters was used with 6 MV flattening filter free (FFF) photon beams delivered by a Varian TrueBeam STx. Non-coplanar conformal arc irradiation was delivered with gantry rotation from 0 to 179 degrees and couch angles of 0, 30, 60, and 90 degrees, resulting in four arc deliveries. The prescribed dose of 10 Gy was defined at the phantom center, corresponding to the linac isocenter, where both the PSD and ionization chamber were positioned. Measurements were performed using a spherical phantom with detectors positioned at the isocenter. Measured doses were compared with treatment planning system (TPS) calculations (Varian Eclipse, AcurosXB).
Results
For all evaluated non-coplanar arc deliveries, the Model 10 demonstrated stable dose measurements with deviations within approximately 1 % relative to the PTW 31016 and TPS calculations. No systematic dependence on couch angle was observed under continuous gantry rotation. The detector response remained stable under small-field and high-dose-rate conditions associated with FFF beams.
Conclusion
The Model 10 exhibited accurate and stable performance for QA measurements under non-coplanar conformal arc irradiation with small fields and high doses per fraction. These results indicate that the evaluated Model 10 is suitable for quality assurance, including PSQA, in non-coplanar stereotactic radiotherapy.