Nuclear Medicine/PET Diagnostic Reference Levels
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On 1 July 2017, new adult Diagnostic Reference Levels (DRLs) were introduced for general nuclear medicine, PET and the CT portion of SPECT/CT and PET/CT procedures.
ARPANSA developed these DRLs together with a liaison panel composed of representatives from the Australian and New Zealand Society of Nuclear Medicine (ANZSNM), the Australasian Association of Nuclear Medicine Specialists (AANMS) and the Australasian College of Physical Scientists and Engineers in Medicine (ACPSEM). The DRLs have been endorsed by the boards of the AANMS and ACPSEM, and the federal council of the ANZSNM.
The DRLs were derived from two data sources. The first data source was a survey of Australian nuclear medicine facilities conducted in 2014/15 (the NDRLS survey). ARPANSA sent invitations to participate in the survey to 175 imaging facilities throughout the ACT, NSW, the NT, SA, Tasmania, and Victoria. The state regulators for Queensland and WA sent invitations to their licensees on behalf of ARPANSA. Seventy-eight facilities participated in the survey, which ARPANSA estimates represents a third of all nuclear medicine facilities within Australia.
We asked participating facility to report every dose (from both radiopharmaceutical and CT sources) delivered within their department over a four week period. The median of the doses delivered at each facility (termed the Facility Reference Level, or FRL) was calculated for each protocol reported. If a facility conducted a procedure four or more times, the FRL was included in the DRL calculation. A DRL was calculated using the NDRLS survey data for all procedures with at least four FRLs. From this data, DRLs for fifteen general nuclear medicine procedures, three PET protocols, three PET/CT scan regions and seven SPECT/CT scan regions were defined.
The second source of data was an extensive survey conducted on behalf of the ANZSNM in 2008 (Diagnostic Reference Activities for Nuclear Medicine procedures in Australia and New Zealand). Rather than request details of individual administrations, the ANZSNM survey asked participants to enter the doses prescribed for each of their protocols. The ANZSNM then published the Most Common Activity (MCA) reported for over 70 different nuclear medicine and PET protocols.
There were a number of protocols listed in the ANZSNM table that did not receive enough data in the NDRLS survey to derive a DRL. In these cases, the ANZSNM data was reanalysed. This accounted for around 50 of the general nuclear medicine DRLs.
The metric chosen to define the DRLs was the 75th percentile of the FRL distribution, keeping the nuclear medicine DRLs consistent with the CT DRLs already published by ARPANSA. In addition to the DRL, the 50th and 25th percentiles of the distributions were also calculated.
For the purposes of meeting the regulatory requirements only the DRL needs to be considered. The other values provide facilities with an indication of the spread of doses delivered and an idea of how low a dose can be achieved while providing adequate image quality for diagnosis.
In 2016, the requirements of the Diagnostic Imaging Accreditation Scheme (DIAS) were amended to include the following provision:
The practice must establish a program to ensure that radiation doses administered to a patient for diagnostic purposes are:
a. annually compared with diagnostic reference levels (DRLs) for diagnostic procedures for which DRLs have been established in Australia; and
b. if DRLs are consistently exceeded, reviewed to determine whether radiation protection has been optimised
In the cases of administered activity in general nuclear medicine and PET (where weight correction is not used), it is ARPANSA's opinion that the above requirement can be met simply by adding the DRL to your facility's written protocol. If the dose specified in the protocol is higher than the DRL, a note on the justification for the higher dose should be included.
For the CT component of multi-modality imaging your facility should perform a yearly audit of the doses delivered. For the audit, the Dose Length Product (DLP) delivered to twenty patients (if feasible) should be recorded, and the median DLP should be compared to the DRL.
A similar audit should be performed in cases where your facility administers an activity that is dependent on the weight of the patient. In the cases where a weight based DRL has been issued (i.e. FDG scans), the fraction of patients who received a dose below the DRL should be calculated (at least half should be under the DRL). In cases where there is a single DRL (for example MPI scans), the median dose delivered in your facility should be compared to the DRL.
For facilities that perform paediatric scans, there are no DRLs and therefore no action is required for DIAS recognition; however, keeping doses as low as practicable while still achieving adequate image quality is still a priority.
Code of Practice for Radiation Protection in the Medical Applications of Ionizing Radiation (RPS 14) - Section 3.1.8 is a clause similar to that in the DIAS requirements, with the exception that no time scale is specified:
The Responsible Person must establish a program to ensure that radiation doses administered to a patient for diagnostic purposes are:
(a) periodically compared with diagnostic reference levels (DRLs) for diagnostic procedures for which DRLs have been established in Australia; and
(b) if DRLs are consistently exceeded, reviewed to determine whether radiation protection has been optimised.
How often the comparison needs to be conducted, and what form that comparison takes, is a matter for the relevant state regulators. However, it is ARPANSA's opinion that the procedures suggested in the 'DIAS requirements' section above will also meet the requirements of RPS 14, Section 3.1.8.
ARPANSA has created a template spreadsheet to help facilities conduct local dose audits. The spreadsheet is intended for dose audits of the CT component of multimodality imaging and for the administration of radioisotopes where the amount of radiopharmaceutical delivered is varied depending on body habitus (for example via weight or BMI).
Further information on International Best Practice for Radiation Protection of Patients can be found on the International Atomic Energy Agency Radiation Protection of Patients website, which can be accessed via the following link: