Quality assurance in brachytherapy: principles for ionization chamber measurement of absorbed dose close to brachytherapy sources.

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.