[The EQUAL-ESTRO external quality control laboratory in France].

PURPOSE: The EQUAL-ESTRO laboratory was set up in 1998 to perform external audits of radiotherapy beams for all the European centres. Until the end of the year 2003, it was funded by EC projects. The external quality control is based on measurements performed with thermoluminescent dosimeters (TLD) sent by postal mail to the participating centre in order to be irradiated on axis in reference conditions and in conditions close to clinical conditions for photon and electron beams. The EQUAL-ESTRO laboratory also started in 2002, a new TLD control allowed to check the dosimetry of complex clinical fields for photon beams with multileaf collimator (MLC). New geometric and dosimetric checks have also been developed for brachytherapy. MATERIAL AND METHODS: The participating centre irradiates TLDs (7LiF: Na, mg, Ti, TLD 937 [Philitec]) in water at a dose of 2 Gy, calculated with the TPS used clinically, following the EQUAL-ESTRO protocol. RESULTS: Since the beginning of the activities, 46% of the French radiotherapy centres and 55% of the European radiotherapy centres applied to participate to the EQUAL quality control programme. In France, the EQUAL-ESTRO laboratory checked, from 1998 and June 2004, 283 photon beams, 180 electron beams and 61 photon beams with MLC. For all the French beams checks, the following results have been observed: for the photon beams, the results show that about 1% of the measured doses in the reference conditions on axis have been detected outside the tolerance level (deviation between the measured dose and the stated dose > +/- 5%) after a first or a second check. For points checked in photon beams with wedge filter, 2.5% of the beams checked show a deviation > +/- 5% after a first or a second check. For the electron beams, the check has been set up in January 1999. For the 180 electron beams checked, 5% of the measured doses in the reference conditions have been found outside the tolerance level (> +/- 5%). CONCLUSION: These results show clearly the importance of the quality control in radiotherapy in the frame of an external audit. This audit should now be a part of a quality assurance programme in the radiotherapy centres in addition to the internal quality control as planned in the French law (02/03/2004) concerning the external quality control conditions of the radiotherapy treatment units.