33. Last results and lessons of the Estro European Network on Quality Assurance in Radiotherapy

Abstract

State of the Art The EQUAL Dosimetry audit service, set-up by the ESTRO in 1998 a , is wellknown through large numbers of TL-dosimeters sent to hospitals to be irradiated in clinically relevant conditions, and read at the EQUAL Measuring Laboratory, IGR, Villejuif. All European countries have now applied to participate (404 centres out of 880) for photon and electron beams. In relation with the IAEA, this service has been extended to 27 centres of 7 countries from Eastern and Central Europe, and the Mediterranean Basin. 757 photon beams and 277 electron beams have been checked according to the “on the beam axis” procedure. Results and outcome – Reference beam output results demonstrating improvements with respect to the former EC Network, and good reliability of the procedure: mean ratios of measured to stated dose of 0.997 (SD 1.8%) for photon beams, and 1.003 (SD 2.1%) for electron beams. – Useful service detecting 7% of the photon beams presenting at least one check point with a deviation > 5% (2% for electron beams, but 3 times more deviations between 3 and 5%). – Re-checks and on-site visits in 8 centres reveal inaccuracies in TPS algorithms or input data and/or in local measurements (wedge factors, collimator aperture factors, PDD's, beams calibrations). Conclusion A number of dosimetric problems are still observed, even on the beam axis. Improvements should be introduced and checked before considering more sophisticated treatment techniques.