In this work we present a new efficient and reliable analytical procedure for evaluation of the Hubbell radiation rectangular source (HRS) integral using a binomial expansion. The proposed procedure guarantees the reliable evaluation of the radiation field generated by a plane isotropic rectangular source (plaque) of scaled width and length a and b, respectively. The formulas obtained are numerically stable for a(2) + b(2) < 1. Numerical results are presented and compared with results using alternative evaluation schemes. (C) 2005 Elsevier Ltd. All rights reserved.