UK Audit of Variation in Nuclear Medicine Occupational Exposure Calculations in 2021

It is a core requirement of UK ionising radiations regulations 2017 (IRR17) compliance for radiation risk assessments and the investigation of accidental exposure scenarios that the magnitude of doses likely to be encountered are evaluated. A novel national audit was undertaken to investigate the variation in dose estimations for a range of foreseeable accidental exposure scenarios in nuclear medicine (NM). Participants were asked to estimate the levels of exposure in 15 foreseeable scenarios; covering whole-body and extremity exposures from external sources, internal exposure and exposures from skin (surface contamination and needle-stick injury) and eye contamination. Questions were intentionally simplified to reduce variation from assumptions made by the participants and to focus more on the underlying gross systematic variation. Twenty-seven centres participated. There was generally a very wide variation in the estimated exposures across all the categories of exposures, apart from internal exposure estimates. Whilst there was no ground truth for each individual question, the variation in results itself often exceeded the relevant threshold for classification and annual dose limits. The majority of variation was due to differences in methods, models and assumptions used by each participant. This audit raises questions around how IRR17 compliance can be universally demonstrated with such wide national variation. It evidences the need for a more standardised practice in NM radionuclide exposure estimates through national consensus guidelines or standards etc.