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 de termination with ionization chambers in the vicinity of brachytherapy sources. In this paper, a modification of the IAEA formalism for exter nal photon beams is proposed in order to make it applicable at a refer ence point 20 mm from brachytherapy sources as well. A non-uniformity correction factor is introduced to correct for the effects of the stee p absorbed dose gradient, and it is concluded that reasonable accuracy is possible when the Bragg-Gray principle is assumed to be valid.