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

alpha-emitting radionuclides provide an effective means of delivering large radiation doses to targeted treatment locations. (RaCl2)-Ra-223 is Food and Drug Administration-approved for treatment of metastatic castration-resistant prostate cancer, and Ac-225 (Ac-225-lintuzumab) radiolabeled antibodies have been shown to be beneficial for patients with acute myeloid leukemia. In recent years, there has been increasing use of alpha-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. Methods: 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 Ac-225. These instruments were placed at 0.32 cm from a 1.0-cm Ac-225 disk source for measurement purposes. Radiation background values, efficiencies, and minimal detectable activities were measured and calculated for each type of detector. Results: The median external measured dose rate from (RaCl2)-Ra-223 patients (n = 611) was 2.5 mu Sv h(-1) on contact and 0.2 mu Sv h(-1) at 1 m immediately after administration. Similarly, Ac-225-lintuzumab (n = 19) patients had median external dose rates of 2.0 mu Sv h(-1) on contact and 0.3 mu Sv h(-1) at 1 m. For the measurement of Ac-225 samples, a liquid scintillation counter was found to have the highest overall efficiency (97%), whereas a ZnS alpha-probe offered the lowest minimal detectable activity at 3 counts per minute. Conclusion: In this article, we report data from 630 patients who were undergoing treatment with the alpha-emitting isotopes Ra-223 and Ac-225. Although alpha-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, alpha-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 alpha-emitters.