Virtual dose mapping allows for accurately determining the radiation dose that a medical device receives during radiation sterilization. One of the important inputs to a dose mapping tool is the full description of the radiation source. For electron and X-ray irradiators this is fairly straight forward as the beam can be simulated as a line source. In gamma irradiation, the devices travel to various dwell positions at which they have different distances and angulation from the ⁶⁰Co source rack. An accurate gamma irradiation model has to take into account the geometric locations of the totes, possible variations of densities within the tote of interest, and the scatter and beam attenuation caused by neighboring totes.   

Dose Insight has a virtual dose mapping tool that allows to import CAD files and the tool’s underlying Monte Carlo simulation engine is Geant4 which has been extensively validated in the scientific community.   

We now configured the Dose Insight simulation tool with a model of a JS 10000 Gamma Irradiation Facility and performed dose studies using a grid phantom as specified in ISO/ASTM 51702:2013 which is used during Operational Qualification of the gamma facility.  

We performed multiple simulations on the grid phantom using operational parameters such as activity variations in the source rack, variations of product in the neighboring totes, and uncertainties in the distances between totes and the distances to the source. We calculated dose uniformity ratios from the grid phantom and tabulated those versus the operational parameters that were used in the simulations. 

We find that simulations are an excellent tool to investigate how sensitive dose uniformity is to the uncertainties and unknowns that are typically seen in gamma irradiation facilities.