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At the present time three most common approaches are used for the planning of the radionuclide therapy: administration of the fixed activity of radionuclide in radiopharmaceutical, or administration of activity normalized per unit of body mass or body surface. That may lead to significant deviations between the prescribed and real absorbed doses in healthy organs and tissues. These deviations are associated with differences in biodistribution and pharmacokinetics of radiopharmaceutical between models and real patients. That does not allow individual planning of the treatment course for each patient since data on the accumulated activity in source regions and organs at risk is limited and uncertainty is too high for the calculation of absorbed doses. Improvements in the reliability of the absorbed dose calculation can be achieved through the use of different imaging modalities (diagnostic nuclear medicine) for the quantitative assessment of accumulated activity of radionuclides in organs and tissues and distribution of radiopharmaceutical in healthy tissues. Planning of radionuclide therapy should be personalized. The current study was aimed at the analysis of the approaches the dosimetry-based planning of radionuclide therapy presented in the Report of International Commission on Radiation Units and Measurements 96 «Dosimetry-guided radiopharmaceutical therapy», differentiated based on the possibilities of the nuclear medicine departments, including examples of levels of planning for most common radiopharmaceuticals. The results of analysis indicated that most optimal approach for Russian clinical practice is to transit to the requirements of planning level 1: to calculate and report administered activity considering patient body mass, type and stage of disease was well as prescribed clinical task. Requirements of planning level 2 are currently impossible to implement nation-wide, except for several nuclear medicine research facilities. Additionally, it is necessary to focus on the development of the methods of estimation of absorbed doses in major delineable organs.

Existing drawbacks of the radionuclide therapy planning may lead to the excessive irradiation of the healthy organs and tissues that is associated with the development of deterministic and stochastic effects. In some cases absorbed dose in region of interest (lesion) can be lower than prescribed therapeutic dose. That reduces the effectiveness of radionuclide therapy and reduces survival rate of patients. These problems are associated with administration of the fixed activity of radionuclide in radiopharmaceutical, or administration of activity normalized per unit of body mass or body surface. That approach does not allow assessing absorbed doses in lesions or healthy tissues for individual patients. Report of International Commission on Radiation Units and Measurements 96 «Dosimetry-guided radiopharmaceutical therapy», published in 2021, presents modern approaches for the dosimetric planning of radionuclide therapy based on the individualized assessment of absorbed doses in organs and tissues. This study was aimed at the analysis of proposed in Report 96 methods of classification of irradiated regions, organs and tissues based on example of radionuclide therapy with 177Lu-DOTATATE. Proposed terms and definitions are harmonized with previous reports of International Commission on Radiation Units and Measurements on external radiation therapy. Terms and definitions analyzed in the current study will be used in the following studies aimed at the development of the requirements on dosimetric planning of radionuclide therapy.

Introduction. Сomputed tomography (CT) is associated with high individual patient doses. Hence, the process of optimization in CT examinations by developing low-dose scan protocols is important.Purpose of the study. Clinical approbation of low-dose protocols developed by the authors earlier, selection of the most promising protocol, assessment of the applicability of the developed algorithm for expert assessment of the quality of CT images.Materials and methods. The study was based on the data from 96 patients who underwent cardiac surgery with suspected infection in the lungs or sternal wound infection. CT examinations were performed using standard, low-dose and ultra-low-dose protocols (effective dose 3,5±0,9, 1,7±0,1 and 0,8±0,1 mSv, respectively) using two iterative reconstruction algorithms (IMR and iDose). The quality of the obtained data was assessed by 5 radiologists with more than 5-year experience in chest radiology.Results. In terms of the number of misinterpretations, no significant differences were estimated between the standard and lowdose protocols for all reconstruction methods. The ultra-low-dose protocol was characterized by a significantly higher number of missing lesions compared to other protocols.Conclusion. The developed method of assessment of the CT image quality has proven to be informative and reproducible and can be used to assess new scanning protocols.