Room: AAPM ePoster Library
Purpose: To accurately model the optical properties of the stem-effect signal in plastic scintillation detectors using Monte Carlo simulation.
Methods: A model of a 1mm diameter, 3m length PMMA light guide was constructed in GEANT4 using specifications from the manufacturer. The relevant optical physics processes were applied to the fiber core, cladding, and aluminum mirror that was fixed to the distal end of the fiber. The input data for the physics processes were obtained from the literature. The optical spectrum exiting the proximal end of the fiber was scored and compared to measured data from a PMMA fiber irradiated with a 6MV photon beam. The optical physics input parameters were iteratively adjusted until agreement was achieved between the simulated and measured optical spectra and the Cerenkov light ratio (CLR). The accuracy of the validated model was tested by comparing simulated and measured data in a 6MV photon beam as functions of magnetic field strength and depth. Field strengths and depths ranging from -1.40T to +1.40T and 1cm to 10cm, respectively, were investigated.
Results: With no optical absorption processes assigned, the simulated Cerenkov spectrum agreed with the known Cerenkov spectrum shape. Agreement within one standard deviation between the simulated and measured spectra were obtained following adjustment of the simulated optical processes. All simulated and measured CLR values were within two standard deviations for all depths and fiber-beam angles tested. Agreement within two standard deviations was observed for all depths and for field strengths ranging from -0.35T to 1.40T. Significant differences between were observed for field strengths ranging from -0.70T to -1.40T, which was attributed to sparse validation data under this irradiation configuration.
Conclusion: With proper validation, it is possible to accurately model the optical response of the stem-effect in scintillators, which has great potential for design optimization of these detectors.