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. Radium-223 dichloride (223RaCl2) is FDA approved for treatment of metastatic castration-resistant prostate cancer (mCRPC) and Actinium-225 (225Ac-Lintuzumab) radiolabeled antibodies have been shown to be beneficial for patients with acute myeloid leukemia. In recent years, there is an 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 three-year period, as well as regulatory requirements and safety practices, are described. Commonly used radiation instrumentation was 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. Results: The median external measured patient dose rate from 223RaCl2 patients (n = 611) was 2.5 µSv hr-1 on contact and 0.2 µSv hr-1 at 1 meter immediately after administration. Similarly, 225Ac-Lintuzumab (n = 19) patients had median external dose rates of 2.0 µSv hr-1 on contact and 0.3 µSv hr-1 at 1 meter. For the measurement of 225Ac samples, a liquid scintillation counter was found to have the highest overall efficiency (97%), while a zinc sulfide (ZnS) alpha probe offered the lowest minimal detectable activity at 3 counts per minute. Conclusion: In this study, we report data from 630 patients who were undergoing treatment with alpha-emitting isotopes 223Ra and 225Ac. While alpha emitters have ability to deliver higher internal radiation dose to the tissues exposed as compared with other unsealed radionuclides, they typically present minimal external dose rate concerns. Additionally, alpha radiation can be efficiently detected with appropriate radiation instrumentation, such as a liquid scintillation counter or ZnS probe, that should be prioritized when surveying for spills of alpha-emitters.