The ICRP Task Group 36 "Radiation Dose to Patients in Diagnostic Nuclear Medicine" is currently working on the revision of ICRP Publication 128 (2015) by updating the dose coefficients using the new ICRP adult and paediatric reference voxel phantoms from ICRP Publications 110 (2009) and 143 (2020), nuclear decay data from Publication 107 (2008) and the dosimetry methodology of ICRP described in Publication 103 (2007). Also the biokinetic information on the radiopharmaceuticals is being updated based on the most recent literature data and will be presented in form of compartmental structures, similarly to what already done by ICRP for workers and members of the public. To assess more realistically the dose to the urinary bladder wall, which is in most cases one of the most exposed tissues, a dynamic bladder model will also be introduced.
Although the quantity effective dose, calculated for a (hypothetical) reference person, is useful (and used) in comparing exposures, and consequently risks, from different radiopharmaceuticals and/or different alternative diagnostic procedures, its application in medicine is controversial and also goes beyond its originally intended purpose. For the specific work of Task Group 36 in diagnostic nuclear medicine it is indeed planned to provide estimates of whole body dose quantities that account for the fact that some investigations are performed on patients of only one sex (e.g., differential diagnosis of prostate cancer with 18F-choline) or in patient groups with anatomical or physiological characteristics differing from the reference persons (for instance, patients with abnormal liver or spleen masses due to diffuse parenchymal disease, or with unilateral kidney blockage).
It is therefore appreciated that the ICRP, in its mission to keep the recommendations fit for purpose, is seeking to revise the concept of the radiation detriment to account for age- and sex-dependence of radiation sensitivity, and to recommend tissue weighting factors which are differentiated accordingly. The idea of no longer referring the effective dose for a hypothetical reference person only, but separately for different subgroups in the population (depending on age, sex, health condition or other characteristics) would actually be very practicable in all medical dosimetric application, including nuclear medicine.
Keywords: nuclear medicine; radiopharmaceuticals; effective dose; dose coefficients