Characterization of Plastic Scintillator Detector for Gamma Knife Beam Profile Measurement: A Comparison with Microdiamond and Film
Abstract
Purpose
To validate the Exradin W2 plastic scintillator for measuring beam profiles in Leksell Gamma Knife (LGK) quality assurance and to compare its characteristics against MicroDiamond detector measurements as a filmless QA alternative.
Methods
The Exradin W2-1x1 scintillator was positioned in the LGK dosimetry phantom using a custom 3D-printed holder to acquire profiles for 4, 8, and 16 mm collimators. Measurements were performed by incrementally shifting the dosimetry phantom and were compared against Treatment Planning System (TPS) data, MicroDiamond, and radiochromic film measurements. Given that shifting the phantom alters the attenuation path length compared to a stationary phantom setup (i.e., film measurement), a simulation study was conducted to quantify the dosimetric differences between "phantom-move" and "detector-move" geometries. Metrics for evaluation included Full Width at Half Maximum (FWHM), penumbra, and 3D isocenter localization.
Results
The W2 detector yielded profile metrics that agreed closely with TPS baselines and film data, with FWHM deviations generally within 0.1 mm across all collimators. Unlike the TPS or MicroDiamond profiles, the W2 measurements exhibited a slight signal elevation in the left tail attributed to a minor stem effect. This effect slightly bends the profile and became more distinct with larger collimator settings. Additionally, the 1 mm active volume length of the W2-1x1 introduced volume averaging effects that slightly impacted the sharpness of the profile falloff compared to high-resolution film. The simulation study confirmed that minor profile variations also exist due to changing attenuation with the phantom-shifting method.
Conclusion
This study demonstrates that the W2 plastic scintillator is a high-precision tool for LGK profile dosimetry, offering accuracy comparable to established methods without the processing overhead of film. While agreement with TPS is excellent, minor characteristics such as the stem effect and volume averaging in the penumbra region are observable but negligible factors in GK QA.