Abstract
Radiopharmaceutical therapy, traditionally limited to refractory metastatic cancer, is being increasingly used at earlier stages, such as for treating minimal residual disease. The aim of this study was to compare the effectiveness of yttrium-90, lutetium-177, indium-111 and terbium-161 at irradiating “micrometastases”. 90Y and 177Lu are widely used beta-emitting radionuclides. 161Tb is a medium-energy beta-isotope, which is similar to 177Lu but emits a higher percentage of conversion and Auger electrons. 111In emits gamma photons, conversion and Auger electrons. METHODS: We used the Monte Carlo code CELLDOSE to assess electron doses from a uniform distribution of 90Y, 177Lu, 111In or 161Tb in spheres with diameters ranging from 10mm to 10µm. Because these isotopes differ in electron energy per decay, the doses were compared assuming that 1 MeV was released per µm3, which would result in 160Gy if totally absorbed. RESULTS: In a 10-mm sphere, the doses delivered by 90Y, 177Lu, 111In and 161Tb were 96.5Gy, 152Gy, 153Gy and 152Gy, respectively. The doses decreased along with the decrease in sphere size, and more abruptly so for 90Y. In a 100-µm metastasis, the dose delivered by 90Y was only 1.36Gy, compared to 24.5Gy for 177Lu, 38.9Gy for 111In and 44.5Gy for 161Tb. In cell-sized spheres, the dose delivered by 111In and 161Tb was higher than that of 177Lu. For instance, in a 10-µm cell, 177Lu delivered 3.92Gy, compared to 22.8Gy for 111In and 14.1Gy for 161Tb. CONCLUSION: 177Lu, 111In and 161Tb might be more appropriate than 90Y for treating minimal residual disease. Terbium-161 is a promising isotope because it combines the advantages of a medium-energy beta-emission with those of Auger electrons, and emits fewer photons than 111In.
- Radiobiology/Dosimetry
- Radionuclide Therapy
- Radiopharmaceuticals
- Radiopharmaceutical therapy
- indium-111
- lutetium-177
- terbium-161
- yttrium-90
- Copyright © 2016 by the Society of Nuclear Medicine and Molecular Imaging, Inc.