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Electron- and Positron-Emitting Radiolanthanides for Therapy: Aspects of Dosimetry and Production

¹ Department of Radiation Physics, Göteborg University, Sahlgrenska University Hospital, Göteborg, Sweden; ² Institute for Nuclear Chemistry, Johannes Gutenberg-University Mainz, Mainz, Germany; and ³ Division of Radiological Chemistry, University Hospital Basel, Basel, Switzerland

Correspondence: For correspondence or reprints contact: Helena Uusijärvi, Department of Radiation Physics, Göteborg University, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden. E-mail: helena.uusijarvi{at}radfys.gu.se

All lanthanides have similar chemical properties regarding labeling. Therefore, radiolanthanides that have been used for therapy, such as ¹⁵³Sm and ¹⁷⁷Lu, might easily be replaced with other radiolanthanides. The aim of this work was to investigate the suitability of electron- and positron-emitting radiolanthanides for radionuclide therapy with reference to dosimetry and production possibilities. Methods: Radiolanthanides with half-lives of 1 h to 15 d, stable or long-lived daughters, and limited photon emission were selected. The ratio of the absorbed dose rate to the tumors and the normal tissue () was calculated for different tumor sizes and compared with the values for ⁹⁰Y and ¹³¹I. The normal tissue and tumors were simulated as an ellipsoid and spheres, respectively. The values depend on the physical parameters of the radionuclides, the tumor size, and the ratio between the activity concentrations in the tumor and normal tissue (TNC). Results: ¹⁵³Sm, ¹⁶¹Tb, ¹⁶⁹Er, ¹⁷⁵Yb, and ¹⁷⁷Lu had the highest values for most of the tumor sizes studied. Among these radiolanthanides, ¹⁶¹Tb and ¹⁷⁷Lu are the only ones that can be produced no-carrier-added (nca) and with high specific activities. The Auger-electron emitters ¹⁶¹Ho and ¹⁶⁷Tm had high values for tumors weighing less than 1 mg and can be produced nca and with high specific activities. ¹⁴²Pr, ¹⁴⁵Pr, and ¹⁶⁶Ho showed values similar to those of ⁹⁰Y. ¹⁶⁶Ho is generator produced and can be obtained nca and at high specific activities. ¹⁴³Pr, ¹⁴⁹Pm, ¹⁵⁰Eu, ¹⁵⁹Gd, ¹⁶⁵Dy, ^176mLu, and ¹⁷⁹Lu had higher values than did ⁹⁰Y for all tumor sizes studied, but only ¹⁴⁹Pm can be produced nca and at high specific activities. The other electron-emitting radiolanthanides and the positron-emitting radiolanthanides showed low values for all tumor sizes because of the high photon contribution. Conclusion: The low-energy electron emitters ¹⁶¹Tb, ¹⁷⁷Lu, and ¹⁶⁷Tm might be suitable for radionuclide therapy. The Auger-electron emitter ¹⁶¹Ho might not be suitable for systemic radionuclide therapy (intravenous injection) because of its short half-life but might be suitable for local therapy (e.g., in body cavities). If higher electron energy is needed, ¹⁴⁹Pm or ¹⁶⁶Ho might be suitable for radionuclide therapy.

Key Words: radiolanthanides • radionuclide therapy • dosimetry • production