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

Abstract

A-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 a-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 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 dose rate from 223RaCl2 patients (n 5 611) was 2.5 mSv h21 on contact and 0.2 mSv h21 at 1 m immediately after administration. Similarly, 225Ac-lintuzumab (n 5 19) patients had median external dose rates of 2.0 mSv h21 on contact and 0.3 mSv h21 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 a-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 a-emitting isotopes 223Ra and 225Ac. Although a-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, a-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 a-emitters.