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Typical effective dose values in nuclear medicine single photon emission imaging in Croatia

Introduction Dose assessment in diagnostic nuclear medicine is required to optimize imaging procedures, estimate radiation risk, improve radiation safety, and verify compliance of local and national practice with international guidelines. Typical effective dose values for a standard patient related to administered radiopharmaceutical were estimated according to results of a study on national diagnostic reference levels for single photon emission imaging procedures. Materials and methods Imaging in nuclear medicine is based on administration of radiopharmaceutical, which is distributed in the patient body. Therefore, International Commission on Radiation Protection (ICRP) has designed a set of mathematical models of the human body to provide estimation of effective dose values delivered by the administered radiopharmaceutical. The methodology proposed by the ICRP assumes that radiation source is whole patient body, and the estimation is based on conversion factors given as radiopharmaceutical specific effective dose per unit of administered activity. The aim of this study was to estimate typical effective dose values for more than 30 single photon emission imaging procedures performed in Croatia by the application of various radiopharmaceuticals based on the radionuclides 99mTc, 131I, 123I and 67Ga. The national practice is represented by typical effective dose values for standard patient with a body mass of 70±20 kg. They were estimated using the median national value of administered activity for each procedure and the corresponding conversion factor. Conversion factors were taken from ICRP publications 60, 80 and 128, except for a few procedures which are omitted from the ICRP publications. Conversion factors for these procedures were taken from respective radiopharmaceutical specification. Results Minimum, maximum and typical national effective dose values related to respective administered radiopharmaceutical were estimated. Effective dose values for the procedures of the same type performed at different nuclear medicine departments were rather heterogeneous, demonstrating values that differ over 10 times between minimum and maximum effective dose values for respective procedure. Values of typical effective dose of investigated imaging procedures vary from less than 0.1 mSv to 35.5 mSv. Such large variations can be related to the different administered activity and desired diagnostic outcome, different radiopharmaceuticals used and different mathematical model adopted. In data analysis and comparison of estimated effective dose values different types of uncertainties should be considered. For example, the uncertainty in effective dose estimates from respective radiopharmaceutical vary among patients due to anatomical likeness to the model (mass of organs and distance between organs) and strongly depends on the mathematical model used for the simulation. It is important to note that periodical performance of comprehensive quality control procedures may enable reduction of uncertainties related to administered activity. Conclusion Estimation of patient effective dose values allows benchmarking of different nuclear medicine procedures in terms of stochastic radiation risk. It also provides a quantity for comparison of respective procedure to other imaging modalities based on the application of ionizing radiation. Additionally, information on the number of such procedures enables determination of the contribution of nuclear medicine imaging to the collective effective dose.

dose assessment, effective dose, single photon emission imaging, radiation risk

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