At present there exists no standardized procedure for absorbed dose determination with ionization chambers in the vicinity of brachytherapy sources. In this paper, a modification of the IAEA formalism for external photon beams is proposed in order to make it applicable at a reference point 20 mm from brachytherapy sources as well. A non-uniformity correction factor is introduced to correct for the effects of the steep absorbed dose gradient, and it is concluded that reasonable accuracy is possible when the Bragg-Gray principle is assumed to be valid.