50 Years of the IAEA/WHO postal dose audit programme for radiotherapy: what can we learn from 13756 results?

Background: The IAEA/WHO postal dose audit programme has been operating since 1969 with the aim of improving the accuracy and consistency of dosimetry in radiotherapy in low-income and middle-income countries world-wide. This study summarises the 50 years' experience of audits and explores the quality of reference dosimetry in participating radiotherapy centres throughout the years.Material and methods: During the IAEA/WHO postal audits the dose determined from the mailed dosimeter is compared with that stated by the participant. Agreement to within ±5% is regarded acceptable whilst deviations outside ±5% limits trigger follow-up actions. Of particular interest in this study was the dependence of clinical dosimetry quality on factors related to the centre infrastructure and expertise in dosimetry of its staff.Results: The IAEA/WHO dose audit programme noted great increase in the overall percentage of acceptable results from about 50% in its early years to 99% at present, although there is some variability of results amongst participating countries. Whereas results for younger radiotherapy machines show the agreement rate between the measured and the stated doses well above 90%, for those over 20 years old the rate dropped to <80%. Linac dosimetry was always better than 60Co dosimetry and multi-machine centres generally performed better than single machine centres equipped with cobalt alone. Second and subsequent participation in audits showed higher quality dosimetry than the first participation. The implementation of modern dosimetry protocols resulted in more accurate dosimetry than the use of the older protocols.Conclusions: Over the 50 years that the IAEA has accumulated dosimetry audit data, practices in radiotherapy centres have significantly improved. Higher quality dosimetry confirmed in audits is generally associated with better infrastructure and adequate dosimetry expertise of medical physicists in participating centres.