Evaluation of a Brachytherapy Hyperspectral Plastic Scintillation System for Gamma Knife Small-Field Dosimetry
Abstract
Purpose
To evaluate the feasibility and accuracy of a hyperspectral plastic scintillation detector (PSD) system (Medscint HYPERSCINT QA-200 with PRB-0019 probe)—commonly used for brachytherapy dosimetry—for Gamma Knife (GK) small-field dosimetry, and to quantify detector and phantom material effects using Monte Carlo (MC) methods.
Methods
EGSnrc simulations were performed for GK 4, 8, and 16 mm collimators in liquid water, Solid Water, ABS, PMMA, and polystyrene (Lucy) phantoms. Dose-to-water output factors and PSD correction factors kPSD=Dw/DPSD were calculated by explicitly modeling the PRB-0019 scintillating volume (≈1 mm × 1 mm) and jacket. Experiments were performed in Solid Water, ABS, and Lucy phantoms using hyperspectral stem-effect correction. Output factors and crossline profiles were measured at isocenter, and sensitivity to sub-millimeter detector offsets and probe rotation was quantified. A subset of measurements was independently benchmarked using EBT3 film.
Results
MC reference output factors (OF) in liquid water were OF4/16 = 0.798 +/- 0.002 and OF4/16 = 0.892 +/- 0.003. MC PSD correction factors were small and collimator dependent, with kPSD (4 mm) = 1.013 +/- 0.003 and kPSD (16 mm) = 1.003 +/- 0.003 in water. Experimental output factors agreed within MC within 1.5%: in Solid Water, OF4/16 = 0.787 +/- 0.008 and OF8/16 = 0.886 +/- 0.007. EBT3 film yielded OF4/16 = 0.792 +/- 0.010 and OF8/16 = 0.882 +/- 0.009, consistent with PSD/MC. For the 4 mm collimator, a 0.5 mm radial mis-centering reduced signal by 11-13%, demonstrating strong sensitivity to positioning. Residual angular dependence after stem correction was less than 1.8%.
Conclusion
Hyerspectral PSD dosimetry provides accurate and practical GK small-field output factor and profile measurements with minimal detector perturbation. EGSnrc modelling supports sub-percent correction requirements and enables robust uncertainty quantification for clinical commissioning and QA, compared to more standard approaches for GK like ion chambers and diodes.