Dosimetric intercomparison at the Scandinavian radiation therapy centres. I. Absorbed dose intercomparison.

A dosimetric intercomparison was carried out at all the centres in Denmark, Norway and Sweden. All the beam qualities (except conventional roentgen rays) used in radiation therapy were investigated. The ratio of the absorbed dose measured by us to that stated by the centre was determined. The mean ratio and standard deviation with the reference field-size were for 60Co gamma beams 1.001 +/- 0.014, for roentgen ray beams (4-45 MV) 1.017 +/- 0.023, electron beams with energy E0 less than 10 MeV 0.989 +/- 0.027, and electron beams with energy E0 greater than or equal to 10 MeV 0.996 +/- 0.034. The difference between the highest and lowest ratios was 17.8 per cent. A systematic difference due to the application of different protocols (NACP 1972 and 1980) was found.