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内容記述 |
Recently, attempts have been made to develop novel agents labeled with alpha-emitting radionuclides for targeted radionuclide therapy (TRT). In Japan in May 2022, an action plan for promoting the production and application of radioisotopes was published in anticipation of the domestic production of medical radionuclides, e.g., 225Ac manufactured from 226Ra. Radiopharmaceuticals containing multiple α-emitting radionuclides, such as 225Ac and 223Ra, have already been investigated in clinical studies and have shown promising therapeutic effects against a wide range of tumors—such as prostate cancer and malignant pleural mesothelioma—that are difficult to treat with conventional therapies. Using preclinical mouse data and a compartment model, we estimated absorbed doses to human tumors and bone marrow and evaluated the effects of 95% labeling efficiency and 5% 226Ra contamination in the 225Ac starting material. To ensure safety, it is important to keep 226Ra contamination below 5%, making it necessary to detect 226Ra at a 5% level relative to 225Ac in the production floors. Therefore, we proposed an on-site alpha spectrometry method that does not require a bulky vacuum chamber and demonstrated its capability to detect 226Ra in 225Ac solution. The minimum detection limit was 1.4 Bq/µl (≈1.4%), confirming that this method can measure contamination levels below 5%. Furthermore, these techniques have potential applications for dose assessment and contamination detection in nuclear emergencies. |
