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.