PURPOSE: To evaluate, in a controlled prospective manner with double-blind read, whether there are differences in interpretations of PET/CT scans at our tertiary medical centre, Rigshospitalet, compared to the external hospitals.

METHODS: Ninety consecutive patients referred to our department who had an external F-18-FDG PET/CT scan were included. Only information that had been available at the time of the initial reading at the external hospital was available at re-interpretation. Teams with one radiologist and one nuclear medicine physician working side by side performed the re-interpretation in consensus. Two oncologists subsequently and independently compared the original reports with the re-interpretation reports. In case of 'major discordance', the oncologists assessed the respective reports validities.

RESULTS: The interpretations were graded as 'accordant' in 43 patients (48%), 'minor discordance' in 30 patients (33%) and 'major discordance' in 17 patients (19%). In 11 (65%) of the 17 cases graded as 'major discordance', it was possible to determine which report that was most correct. In 9 of these 11 cases (82%), the re-interpretation was most correct; in one case, the original report and in another case, both interpretations were incorrect.

CONCLUSIONS: Major discordant interpretations were frequent [19% (17 of 90 cases)]. In those cases where follow-up could assess the validity, the re-interpretation at Rigshospitalet was most correct in 9 of 11 cases (82%), indicating that there is a difference in expertise in interpreting PET/CT at a tertiary referral hospital compared to primary local hospitals.