The ESTRO-EQUAL Quality Assurance Network for photon and electron radiotherapy beams in Germany

Background: In 1998 an ESTRO Quality Assurance Network for radiotherapy (EQ UAL) has been set up for 25 European countries for photon and electron beam s in reference and non-reference conditions. Material and Methods: Measurements are done using LiF powder (DTL937-Philit ech, France) that is processed with the PCL3 automatic reader (Fimel-PTW). The participating centers irradiate the TLDs with an absorbed dose of 2 Gy according to the clinical routine. Results: Until September 2000 EQUAL has checked 135 photon beams (including the beams rechecked) from 51 radiotherapy centers in Germany out of 86 acc epted centers. The results show that 2% of the beam outputs in reference co nditions and 3% of the percentage depth doses are outside the tolerance Lev el (deviation > +/- 5%). 6% of the beam output variations and of the wedge transmission factors show deviations > +/- 5%. The global analysis of resul ts shows deviations greater than or equal to +/- 5% in at Least one paramet er for 18 beams out of the 135 beams checked. Five rechecked beams present one "real dosimetric" problem in one or more parameters, corresponding to 4 % of the 114 beams for which the deviations cannot be attributed to set-up errors. - The EQUAL network has checked 89 electron beams in Germany. The r esults show that all. beam outputs checked are within the tolerance Level. The standard deviation for the beam output in reference conditions is 2.0% and 2.2% for the beam output for the others field sizes. The percentage of deviations > 3% and less than or equal to 5% for the reference beam output is higher for electron beams than for photon beam checks. Therefore the ele ctron beam calibration and the TPS algorithms should be improved to increas e the accuracy of the patient dosimetry for radiotherapy. Conclusion: EQUAL program demonstrates a consistency in radiotherapy dosime try for photon and electron beams resulting in a satisfying accuracy of the dosimetry in Germany.