Compiling data on radiopharmaceutical dosimetry for diagnostic nuclear medicine inevitably leads to the question of up-to-date minimum standards for collecting reliable data for dosimetry. In principle, the steps described in MIRD Pamphlet No. 16 [7
], ICRU 67 [110
] and the EANM dosimetry guidance document on good dosimetry reporting [4
] should be considered. State-of-the-art dosimetry today includes the use of CT systems for attenuation correction, scatter correction, consideration of the duration of the study depending on the biokinetics of the radiopharmaceutical and of bladder voiding intervals, a calculation of residence times including an analysis of the errors associated with the respective calculation method and the appropriate use of phantoms for calculating EDs. As the number of subjects in many biokinetic and dosimetric studies is fewer than 10 the question of the validity of the data for a larger population needs to be addressed. In the scope of the new ICRP recommendations [9
] (ICRP 103) gender-specific differences might also need to be considered in the future.
In some cases it was very difficult to find data on biokinetics and dosimetry, especially for radiopharmaceuticals that changed their name during the approval phase. For example, it was not clear at first glance that 123I-Ioflupane and 123I-FP-CIT are identical. The same applies to 99mTc-HMPAO and 99mTc-exametazime. For some radiopharmaceuticals with marketing authorization such as 99mTc-antigranulocyte no peer-reviewed articles containing dosimetry data have been published; thus the quality of the underlying experimental data cannot be assessed. For 18F-fluoride, a more frequently used PET radiopharmaceutical, no whole-body quantitative imaging data are available, and the biokinetic models rely only on compartment models (based on blood and urinary excretion) and/or local quantitative images. For 68Ga-DOTATATE no published data on dosimetry are available.
For some radiopharmaceuticals the biokinetic data were acquired more than 20 years ago (e.g. 67
Tc-sestamibi, and 18
F-fluoride). Due to considerable improvements in nuclear medicine equipment over the years, an improved assessment of the absorbed doses seems warranted and would be of scientific interest. For 201
Tl-chloride, a recalculation of the absorbed doses in ICRP 106 [3
] following reevaluation of the available data on testicular uptake led to a substantially decreased ED compared to ICRP 80 [2
] (11 mSv vs. 17 mSv with an administered activity of 75 MBq).
Dosimetry data for paediatric nuclear medicine applications of radiopharmaceuticals are sparse. In the case of missing paediatric data, the ICRP reports use the biokinetics obtained in adults and paediatric age-dependent mathematical phantoms. As the size and weight of children and adolescents vary considerably and show only a poor correlation with age, the dose coefficients (listed in the ICRP publications) should be adjusted according to weight instead.
The latest publication of the ICRP on absorbed doses for radiopharmaceuticals (ICRP 106) [3
] still applies the tissue weighting factors given in ICRP 60 [10
]. The 2007 ICRP recommendations (ICRP 103) [9
] now clearly demand the use of male and female reference voxel phantoms which were published in ICRP 110 [111
]. The new concept demands a determination of the equivalent doses to the organs and tissues of the reference male and the reference female separately. In order to obtain the equivalent doses to the reference person, the gender-specific equivalent doses are averaged; hence the new tissue weighting factors can be applied. Moreover, according to ICRP 103, only the latest ICRP voxel phantoms should be used for the calculations of ED. Applying the new weighting factors to a set of equivalent organ doses previously calculated with a mathematical phantom will therefore not result in a correct ED value due to ICRP 103. Presently, the modified tissue weighting factors and the subsequent calculation of the ED according to the formalism of ICRP 103 cannot be applied to nuclear medicine as the S-values for radiopharmaceuticals using the new recommendations of the ICRP are still missing.
As, in many cases, the dosimetry protocols applied for a given radiopharmaceutical are very heterogeneous with respect to the time-points and bladder voiding, and to the dose assessment after the last data point (e.g. for 18F-choline, 18F-FDG, 99mTc-ECD and 99mTc-HMPAO). Therefore, the development of more uniform protocol templates for diagnostic nuclear medicine dosimetry is required.
In many articles the description of the methodology and the reporting of the results are incomplete so that it is difficult to get information for reassessment of absorbed doses. In future articles the use of the suggestions given by the EANM guidance document on good dosimetry reporting [4
] is strongly recommended.
For most diagnostic radiopharmaceuticals dosimetry data are available, although the data collection and calculation methods are heterogeneous. As some of the data were acquired more than 20 years ago, it would be of interest to generate new data on biokinetics and dosimetry in diagnostic nuclear medicine using state-of-the art equipment and more uniform dosimetry protocols. Data for paediatric nuclear medicine are missing in most cases.
As some of the references collected for this review are not easily accessible a major conclusions of this work is that, for easier public access to dosimetry data of diagnostic radiopharmaceuticals, a database containing these data should be created and maintained.