Methods and an apparatus for determining a radiation dosage received by a product being exposed to radiation in an irradiator cell through a computer simulation are provided. One exemplary method includes a computer simulation for determining radiation dosages received by a product to be passed along a radiation cell, where the product is to be stationary at a set number of locations within the cell is provided. The method initiates with a point on the product being defined. Then, pre-calculated lengths between the point on the product and the radiation source at each of the set of locations in the cell are identified. Next, a dosage of radiation to be received by the point on the product at each location is calculated using the pre-calculated lengths.