The ESTRO-QUALity assurance network (EQUAL)

Background and purpose: ESTRO has set up a Quality Assurance network (EQUAL ) to check the dose delivered on axis in reference and non-reference condit ions for external radiotherapy. The external audits covered by the network are based on measurements made with mailed thermoluminescent dosimeters (TL D). Material and methods: The TLD consist of LiF powder type DTL 937 read with a PCL 3 automatic TLD reader. The participating centres ale instructed to d eliver to the TLDs absorbed doses of 2 Gy calculated with the Treatment Pla nning System used in clinical routine. A maximum of three photon energies b y participating centre have been checked with 10 on-axis points per beam. T he quantities checked include the reference beam output, beam output variat ion with collimator opening. depth dose data and wedge transmission factor. Results: During the 1998 EQUAL programme 102 centres have been checked corr esponding to 235 beams (28 Co-60 beams and 207 X-ray beams). About 3% of th e outputs in reference conditions show deviations outside tolerance level ( > +/-58). A similar rate of deviation is noted for the: percentage depth do ses. A rate of deviation (6%) has been observed for the beam output variati on (open and wedged beams) and the wedge transmission factor. The analysis of the results shows that for 24 out of the 102 centres, a deviation outsid e tolerance level is observed at least in one point. mainly for the large a nd rectangular field sizes and for the wedged beams. Conclusions: The results for the EQUAL programme show the importance of a q uality assurance network in Radiotherapy especially for the non reference p oints even if they are only located on the beam axis (In order to participa te in this network, please contact EQUAL secretariat or download the attach ed application form ESTRO web site: Dr I.H. Ferreira or Mrs Aline Mechet, E QUAL-ESTRO, Physics Department. Institut Gustave-Roussy 39 Rue Camille Desm oulins, F-94805 Villejuif Cedex, France. e-mail:equal@igr.fr or http://www. estro.be/). (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.