Abstract
2080
Background: The use of Lutetium 177 (Lu 177), a beta emitter, as a therapeutic radionuclide is growing. Lutetium Lu 177 Dotatate (Lutathera®) is a new Peptide Receptor Radiotherapy (PRRT) recently approved by the FDA for neuroendocrine tumors. When assaying beta emitters in a dose calibrator, there may be production of low electromagnetic energies due to direct decay properties or via Bremsstrahlung. Container types and geometries can affect the dose calibrator assay of any radionuclide, especially those that produce low electromagnetic energy. Lu 177 emits high energy beta particles with an Eβ max = 497 keV (78.6 %), 384 keV (9.1 %) and 176 keV (12.2 %), and gamma photons Eγ = 208keV (11.1%), 113 keV (6.6%). There are also multiple low energy x-rays (65 keV or less), but emitted a small percent of time. The aim of this study is to understand the effects of container types and geometries during a Lu 177 assay. Materials/Methods: A CRC® dose calibrator was used to assay Lu 177. Multiple tests were performed to determine the effects of different container types, such as glass and plastic, on dose calibrator readings. The dose calibrator readings of a 5ml plastic syringe, 10ml plastic syringe, 12 ml plastic syringe, 20ml plastic syringe, and a small glass vial were compared to a large glass vial (Lutathera® vial). This was repeated two more times. Effects on geometry were determined by assaying Lu 177 in a 20ml plastic syringe and consecutively adding 3 ml of saline solution (0.9% NaCl). The starting total volume was 3 ml and the ending total volume was 15 ml. This was also repeated two more times.
Results: The percent differences between the large glass vial and the plastic syringes were: 5ml plastic syringe 4.61%, 10ml plastic syringe 1.67%, 12 ml plastic syringe 2.22%, and 20 ml plastic syringe 4.11%. The percent difference large glass vial and small glass vial was 0.03%. For geometry assessment, the average percent difference for all volumes was 0.75%. Conclusion: Results show that neither the container type nor geometry has a significant effect on dose calibrator readings when assaying Lu 177. The gamma photons at Eγ = 208keV (11.1%), 113 keV (6.6%) most likely contribute to the ionization in the dose calibrator and are not greatly affected by container type and geometry. Hence, one calibration number on the dose calibrator could be used to assay Lu 177. References: Dash, A., Raghavan Ambikalmajan Pillai, M., & Knapp Jr., F. (2015, February 17). Production of 177Lu for Targeted Radionuclide Therapy: Available Options. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4463871/pdf/13139_2014_Article_315.pdf
