A DOSIMETRIC INTERCOMPARISON OF KILOVOLTAGE X-RAYS, MEGAVOLTAGE PHOTONS AND ELECTRONS IN THE REPUBLIC-OF-IRELAND

Background and purpose: A comprehensive dosimetry intercomparison has been carried out involving all the radiotherapy centres, all external beam modalities and every radiotherapy treatment unit in the Republic of Ireland. Materials and methods: Reference point measurements were m ade for all megavoltage photon beams. Doses were also investigated in planned three-field distributions. One of these was in a homogeneous e poxy resin solid water phantom, whilst the second included a lung equi valent insert. The intercomparison was also carried out for three elec tron energies in each centre. The position of the depth of maximum dos e for a standard field size was independently determined, as was the b eam energy and a subsequent beam calibration was made. In addition, a kilovoltage X-ray intercomparison was carried out on every kilovoltage quality. Results: For 13 megavoltage photon beams a mean ratio of int ercomparison measured dose to locally measured dose of 1.002 was obtai ned (standard deviation 1.2%). For 12 electron beam:measurements a mea n ratio of intercomparison measured dose to locally measured dose of 1 .018 was obtained (standard deviation 0.8%). For four kilovoltage beam s a mean ratio of intercomparison measured dose to locally measured do se of 0.997 was obtained (standard deviation 1.9%). Conclusions: The i ntercomparison has given confidence in the basis of clinical delivery of radiation dose in radiotherapy treatment and in the consistency (pr ecision) of dosimetry between different centres within the Republic of Ireland. In addition, it has established a methodology for subsequent ongoing routine radiotherapy dosimetry audit and a baseline set of re sults to act as an initial reference point. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.