Is Dosimetry Necessary in Radionuclide Therapy of Patients with Metastases?

Purpose: Analysis of modern approaches to dosimetric support of radionuclide therapy at the technological stages of dosimetric planning, hospitalization and evaluation of treatment effectiveness. Material and methods: A comparative analysis of the methodological specifics of dosimetric support of radionuclide therapy with the introduction of radiopharmaceuticals into the body and conventional radiation therapy using sealed sources of ionizing radiation was carried out. Two methodologically different approaches to dosimetric planning of the level of internal irradiation from a radiopharmaceutical introduced into the patient’s body are considered. The features of radiation monitoring are discussed both for the patient’s stay in the radionuclide therapy department and his/her safe discharge from the department for others, and for the removed solid and liquid radioactive waste. A comparative analysis of the functional capabilities of various criteria for assessing the long-term and short-term effectiveness of radionuclide therapy of bone metastases was carried out. Focal absorbed doses of internal irradiation are considered as one of the criteria, for the determination of which a method for their calculation is proposed based on the MIRD formalism and quantitative data from SPECT/CT scanning of an X-ray phantom and a real patient who has been administered a β-γ-emitting therapeutic radiopharmaceutical. Results: Using a clinical example of radionuclide therapy with 177Lu-PSMA-617 in a patient with stage 4 prostate cancer, dose estimates of internal irradiation of bone metastases by β-particles were obtained. The obtained dosimetric data were compared with efficiency estimates based on metabolic, hematological, hormonal and biochemical parameters, as well as the tumor marker PSA. Conclusion: Unlike conventional radiation therapy, dosimetric support for planning and evaluating the effectiveness of treatment has not yet become a fundamental methodological basis for modern radionuclide therapy.