External audits of electron beams using mailed TLD dosimetry: preliminary results

Aim: A feasibility study has been performed to investigate the possibility of using mailed thermoluminescence dosimetry (TLD) for external audits of c linical electron beams in Europe. Methods: In the frame of the EC Network Project for Quality Assurance in Ra diotherapy, instruction sheets and mailing procedures have been defined for mailed TLD dosimetry using the dedicated holder developed by a panel of ex perts of the International Atomic Energy Agency (IAEA). Three hundred and t hirty electron beam set-ups have been checked in the reference centres and some local centres of the EC Network Project and in addition through the ce ntres participating to the EORTC Radiotherapy Group trial 22922. Results: The mean ratio of measured dose to stated dose is 0.2% and the sta ndard deviation of measured dose to stated dose is 3.2%. In seven beam set- ups, deviations greater than 10% were observed (max. 66%), showing the usef ulness of these checks. Conclusion: The results of this feasibility study (instruction sheets, mail ing procedures, holder) are presently endorsed by the EQUAL-ESTRO structure in order to offer in the future to all ESTRO members the possibility to re quest external audits of clinical electron beams. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.