154 - Quality assurance network in central Europe: External audit on output calibration for photon beams

Abstract

The EROPAQ project for TLD monitoring of photon beams started in June 1994 with the set-up of the TLD system: calibration, reading and evaluation procedures. The acceptance level of ±3% was set for the TLD intercomparisons. The policy of the project was to check all beams in 47 participating radiotherapy centres and to recheck all the beams in those centres, where a deviation exceeding ±3% occurred in one or more of the beams. Out of 129 beams checked, 100 beams (78%) were found within the ±3% limit. Eleven beams show deviations larger than ± 6%, and immediate corrective action was undertaken. Out of 47 centres checked, 22 did not participate in any external audit in a preceding 5 years. In these centres 68% (34/50) of the total number of γ and x-ray beams checked but only 59% (20/34) of γ beams were within the acceptance level, while in the 25 centres, which participated in an external audit before, these figures were 84% (66/79) and 88% (35/40) respectively. The sources of discrepancies were thoroughly ...