Since 2010, positron emission tomography/magnetic resonance (PET/MR) has been increasingly used as clinical routine in nuclear medicine departments. One advantage of PET/MR over PET/computed tomography (CT) is the lower dose of ionising radiation delivered to patients. However, data on the radiation dose delivered to staff operating PET/MR compared with the new generation of PET/CT equipment are still lacking. Our aim was to compare the radiation dose to nuclear medicine technologists performing routine PET/MR and PET/CT in the same department. We retrospectively measured the daily radiation dose received by PET technologists over 13 months by collecting individual dosimetry measurements (from electronic personal dosimeters). Data were analysed taking into account the total number of studies performed with each PET modality (PET/MR with Signa 3T, General Electric Healthcare versus PET/CT with Biograph mCT flow, Siemens), the type of exploration (brain versus whole-body PET), the18F activity injected per day and per patient as well as the time spent in contact with patients after tracer injection. Our results show a significantly higher whole-body exposure to technologists for PET/MR compared with PET/CT (10.3 ± 3.5 nSv versus 4.7 ± 1.2 nSv per18F injected MBq, respectively;p< 0.05). This difference was related to prolonged contact with injected patients during patient positioning with the PET/MR device and MR coil placement, especially in whole-body studies. For an equal injected activity, radiation exposure to PET technologists for PET/MR was twice that of PET/CT. To minimise the radiation dose to staff, efforts should be made to optimise patient positioning, even in departments with extensive PET/CT experience.

Since october 2015, PET/MR has been used extensively for clinical routine in the nuclear medicine department of the Pitié-Salpêtrière Hospital (Paris, France) with a throughput of 11 to 15 patients each day. While many studies have been conducted to investigate dose reduction strategies to patients with hybrid PET/MR devices, no study has focused on staff radiation safety. Knowing that patient positioning within the scanner takes longer in PET/MR than in PET/CT because of the placement of several local MR receive coils, a retrospective study was carried out to measure the radiation doses to nuclear medicine technologists from the patient. The analysis was conducted during one year on 1332 clinical PET/MR studies performed with the Signa PET/MR system (General Electric Healthcare) in our department. The whole-body exposure of the technologist staff was on average for all PET/MR exams10.3 ± 4 nSv per injected MBq of 18 F. When performing brain PET/MR exams only, the whole-body exposure was on average 8.7 ± 2 nSv per injected MBq of 18 F. Brain PET/MR provides lower radiation dose than whole-body examinations for cancer screening due to a lower injected activity (2 vs. 3 MBq kg-1) and shorter patient positioning (5 vs. 15 min). When starting PET/MR in a nuclear medicine department, an important step is to optimise patient positionning within the scanner to minimise radiation dose received by the technical staff from patients.