Swiss survey on hybrid imaging CTs doses in Nuclear Medicine and proposed national dose reference levels.

A multidisciplinary working group led by the Swiss Federal Office of Public Health was formed to plan and perform a nationwide survey of patient radiation exposure from computed tomography (CT) in hybrid devices across Nuclear Medicine departments. The survey included 16 departments (of which 5 were university hospitals) and the submitted responses included 10,673 entries for the 33 different protocols proposed (11 in PET and 22 in SPECT). The working group determined the selection and exclusion criteria applied to the analysis. This work presents the survey preparation and data analysis including the exclusion criteria used. The results are used to inform recommendations for National Diagnostic Reference Levels (DRL) for CT procedures in Nuclear Medicine in Switzerland. Of the 33 protocols initially proposed, 10 protocols for both PET and SPECT modalities were retained after exclusion criteria and thresholds were applied. The results obtained in terms of volume-weighted computed tomography dose index (CTDIvol) and dose length product (DLP) have been put forward as recommendations for national Diagnostic Reference Levels for protocols in hybrid imaging devices in Nuclear Medicine in Switzerland and will be published by the Federal Office of Public Health.

Intercomparison of activity measurements for beta-emitters in Swiss nuclear medicine laboratories.

OBJECTIVE: The activity of injected radiopharmaceuticals in nuclear medicine, including beta-emitters used for pain palliation, has to be monitored systematically. The objective of the present work was to evaluate the situation and precision of activity monitoring for beta-emitters in Swiss nuclear medicine laboratories. METHODS: A questionnaire about the monitoring methods used was sent to 50 centers. On the basis of the questionnaire results, an intercomparison of activity measurements with 90Y and 169Er sources was organized. RESULTS: This study showed that most laboratories check beta-emitter activity with a dose calibrator measurement in the original vial provided by the producer or in the injection syringe. They therefore need to have calibration factors for the corresponding measurement geometries. The results of the intercomparison were disappointing overall. Sixteen of 27 90Y measurements and 17 of 22 169Er measurements in the original vial deviated from the reference activity by more than 20%. The situation was similar for the syringe. These discrepancies did not stem from the intrinsic limitation of the measuring method but were mainly attributable to the poor quality of the calibration factors provided by the manufacturers, in addition to lack of follow-up and incorrect background subtraction, particularly for 169Er, by the nuclear medicine laboratories. Manufacturers are being contacted to discuss possible improvements for the situation. CONCLUSION: This study showed that commercial dose calibrators are generally adequate for measurement of the activities of beta-emitters. However, in some cases, the measurement of 90Y can lead to errors reaching +/-50%. For 169Er, with its much lower beta-energy, the situation is even worse; the observed differences can be higher than 1 order of magnitude.