Radiation Safety Considerations and Clinical Advantages of α-Emitting Therapy Radionuclides

Abstract

<b>CE credit:</b> For CE credit, you can access the test for this article, as well as additional <i>JNMT</i> CE tests, online at https://www.snmmilearningcenter.org. Complete the test online no later than March 2025. Your online test will be scored immediately. You may make 3 attempts to pass the test and must answer 75% of the questions correctly to receive Continuing Education Hour (CEH) credit. Credit amounts can be found in the SNMMI Learning Center Activity. SNMMI members will have their CEH credit added to their VOICE transcript automatically; nonmembers will be able to print out a CE certificate upon successfully completing the test. The online test is free to SNMMI members; nonmembers must pay $15.00 by credit card when logging onto the website to take the test. α-emitting radionuclides provide an effective means of delivering large radiation doses to targeted treatment locations. ²²³RaCl₂ is Food and Drug Administration–approved for treatment of metastatic castration-resistant prostate cancer, and ²²⁵Ac (²²⁵Ac-lintuzumab) radiolabeled antibodies have been shown to be beneficial for patients with acute myeloid leukemia. In recent years, there has been increasing use of α-emitters in theranostic agents with both small- and large-molecule constructs. The proper precautionary means for their use and surveying documentation of these isotopes in a clinical setting are an essential accompaniment to these treatments. <b>Methods:</b> Patient treatment data collected over a 3-y period, as well as regulatory requirements and safety practices, are described. Commonly used radiation instruments were evaluated for their ability to identify potential radioactive material spills and contamination events during a clinical administration of ²²⁵Ac. These instruments were placed at 0.32 cm from a 1.0-cm ²²⁵Ac disk source for measurement purposes. Radiation background values, efficiencies, and minimal detectable activities were measured and calculated for each type of detector. <b>Results:</b> The median external measured dose rate from ²²³RaCl₂ patients (<i>n</i> = 611) was 2.5 μSv h⁻¹ on contact and 0.2 μSv h⁻¹ at 1 m immediately after administration. Similarly, ²²⁵Ac-lintuzumab (<i>n</i> = 19) patients had median external dose rates of 2.0 μSv h⁻¹ on contact and 0.3 μSv h⁻¹ at 1 m. For the measurement of ²²⁵Ac samples, a liquid scintillation counter was found to have the highest overall efficiency (97%), whereas a ZnS α-probe offered the lowest minimal detectable activity at 3 counts per minute. <b>Conclusion:</b> In this article, we report data from 630 patients who were undergoing treatment with the α-emitting isotopes ²²³Ra and ²²⁵Ac. Although α-emitters have the ability to deliver a higher internal radiation dose to the exposed tissues than can other unsealed radionuclides, they typically present minimal concerns about external dose rate. Additionally, α-radiation can be efficiently detected with appropriate radiation instrumentation, such as a liquid scintillation counter or ZnS probe, which should be prioritized when surveying for spills of α-emitters.

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