Intercomparison of calibration procedures for Ir-192 HDR sources in Brazil

The lack of well established dosimetry protocols for HDR sources is a point of great concern regarding the uniformity of procedures within a particula r country and worldwide. The main objective of this paper is to report the results from ten institutions of an intercomparison of calibration procedur es for Ir-192 HDR sources currently in use in Brazil. The treatment irradiator of one institution was calibrated by a reference s ystem and used by all participants with their own measuring electrometers a nd ionization chambers under the same experimental conditions. Two methods were used: the calibration jig and the well-type ionization chamber. Each p articipant was allowed to use their own method and formalism. The results of this exercise were very positive since this was the first ti me in Brazil that a group of users gathered to share their experience and o penly discuss the physical concepts behind the calibration procedures. The results were all within +/- 3.0%, except one case where -4.6% was observed and later identified as a problem with the N-k value for x-rays. Though the magnitude of the deviations found was generally acceptable consi dering the diversity of formalisms currently in use, a proposal is now bein g prepared to be adopted as a national protocol. The identification of the institutions was left out for the sake of confide ntiality.