ScintSim1 : A new Monte Carlo simulation code for transport of optical photons in 2D arrays of scintillation detectors

Abstract

Two-dimensional (2D) arrays of thick segmented scintillators are of interest as X-ray detectors for both 2D and 3D image-guided radiotherapy (IGRT). Their detection process involves ionizing radiation energy deposition followed by production and transport of optical photons. Only a very limited number of optical Monte Carlo simulation models exist, which has limited the number of modeling studies that have considered both stages of the detection process. We present ScintSim1, an in-house optical Monte Carlo simulation code for 2D arrays of scintillation crystals, developed in the MATLAB programming environment. The code was rewritten and revised based on an existing program for single-element detectors, with the additional capability to model 2D arrays of elements with configurable dimensions, material, etc., The code generates and follows each optical photon history through the detector element (and, in case of cross-talk, the surrounding ones) until it reaches a configurable receptor, or is attenuated. The new model was verified by testing against relevant theoretically known behaviors or quantities and the results of a validated single-element model. For both sets of comparisons, the discrepancies in the calculated quantities were all <1%. The results validate the accuracy of the new code, which is a useful tool in scintillation detector optimization.

Modelling the transport of optical photons in scintillation detectors for diagnostic and radiotherapy imaging

“…In addition to providing various quantities during the transport of the scintillation light within the detector element, the outputs include the number and spatial distribution of the optical photons reaching the optical receptor. The code was revised and rewritten later in the MATLAB environment, expanded to add the ability to model a 2D array of coated detector elements each in the shape of a rectangular parallelepiped with optical crosstalk, and called ScintSim1 (Mosleh-Shirazi et al , 2014a). The updated code (ScintSim2) includes the ability to model divergent 2D arrays of coated detector elements (Mosleh-Shirazi et al , 2014b).…”

“…Experimental validation of the relative light outputs of individual scintillator cubes with different materials (CsI(Tl), BGO and ZnWO 4 ) and coatings (specular and Lambertian) was also presented. For the subsequent developments of the code (Mosleh-Shirazi et al , 2014a; Ranjbar, 2015), individual optical modules were checked against theory and the results of the first version.…”

“…Conclusions are then made without accounting for light transport or, in some cases, using non-validated or not fully disclosed optical models. Including proper light transport in simulations, such as light absorption and scattering in the detector, crystal microstructure, scintillator coating type and reflectivity, and angular distribution of the light exiting the crystal, will affect some parameters that may influence detector or system optimization (Mosleh-Shirazi et al , 1998a; Badano and Sempau, 2006; Monajemi et al , 2006; Wang et al , 2009; Roncali and Cherry, 2013; Mosleh-Shirazi et al, 2014a, 2014b; Nillius et al , 2015). The significantly limited availability and specialized nature of optical MC code compared to ionizing radiation MC packages has contributed to their less frequent use.…”

“…(Mosleh-Shirazi et al , 1998a; Roncali et al , 2014). However, in some general-purpose optical MC codes, detailed information on quantities of interest describing the history of the light rays are not always accessible, making in-house codes with complete access and flexibility still attractive (Mosleh-Shirazi et al , 2014a). …”

“…Experimental validation of the latter model, its applications, updated versions and further benchmarking have also been reported (Mosleh-Shirazi et al , 1998a, 2014a, 2014b; Ranjbar, 2015). Optimization of other types of segmented crystalline detectors using optical MC modelling has also been a topic of interest (Monajemi et al , 2006; Wang et al , 2009), as has optical MC simulation for dosimetric use of EPID images (Blake et al , 2013).…”