The Efficacy of Radionuclide Therapy for Bone Metastasis

Purpose: Development of a methodology for evaluating the effectiveness of radionuclide therapy for bone metastases based on dosimetric and clinical and laboratory criteria. Material and methods: A comparative analysis of the functionality 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 exposure are considered as one of the criteria, for the determination of which a simplified method for their calculation is proposed based on quantitative data from SPECT/CT scanning of an X-ray phantom and a real patient who has been injected with a β-γ-emitting therapeutic radiopharmaceutical. Results: On a clinical example of radionuclide therapy with 177Lu-PSMA-617 in a patient with stage 4 prostate cancer, dose estimates of internal irradiation of foci with β-particles were obtained. Calculations were made for bone metastases of 7 localizations in dynamics for each of the 5 fractions of the course of radionuclide therapy. It is shown that the total focal doses for 5 fractions of internal exposure vary from 70.6 to 116.8 Gy for different foci, which corresponds to the literature data obtained by more accurate methods of dosimetry of internal exposure. The obtained dosimetric data were compared with efficacy estimates based on metabolic, hematological, hormonal and biochemical parameters, as well as on the tumor marker PSA. Conclusion: The main criterion for assessing the antitumor efficacy of radionuclide therapy is the metabolic activity of bone foci, while data on the accumulated focal doses of internal β-irradiation are of an auxiliary nature. Hematological indicators should be the criteria for assessing radiotoxicity and used to adjust the course of radionuclide therapy.