A Simulated Annealing optimization technique to obtain uniform dose distribution in gamma irradiators

It is important to achieve dose uniformity in product box irradiated by gamma irradiators. To minimize lateral non-uniformity of absorbed dose, quantified as Dose Uniformity Ratio in a particular plane (DURp), activities of source pencils need to be optimized. In present study, Simulated Annealing technique is used for this purpose and the same is described for a Low-Dose 60Co Blood Irradiator. An in-house computer program is developed that calculates DURp and optimizes the activities of source pencils. The study demonstrates that only the primary component of dose is sufficient to determine DURp. In the Simulated Annealing technique, several cooling parameters are tested and the most effective cooling schedule is selected to obtain optimized activity distribution. An improvement of 22% in DURp value is observed after optimization as compared to each source pencil having the same activity. The methodology described in the paper is efficient as optimization of source activities using a trial-and-error approach will be tedious and time consuming. The optimization methodology described in the study is applicable to any irradiator geometry. However, geometry-specific dose calculation approach should be adapted.