161Tb-labeled somatostatin peptides delivered 3.6-3.8 times higher nuclear radiation doses than their 177Lu counterparts, primarily due to internal conversion electrons rather than Auger electrons.
3.8× nuclear dose161Tb-DOTA-LM3 delivered 3.8 times more radiation to cancer cell nuclei than the standard 177Lu version, primarily through internal conversion electrons that bridge the distance from cell surface to nucleus
What the researchers found
161Tb-DOTATATE and 161Tb-DOTA-LM3 delivered 3.6× and 3.8× higher nuclear absorbed doses than 177Lu-labeled counterparts. The enhanced dose was primarily from internal conversion electrons, not Auger electrons. 161Tb-DOTA-LM3 showed a superior linear-quadratic dose response (suggesting additional membrane damage) compared to the linear-only response of 161Tb-DOTATATE.
Why it matters
177Lu-DOTATATE is already an approved, effective treatment for neuroendocrine tumors. If 161Tb can deliver 3-4 times more radiation to tumor cell nuclei using the same targeting peptides, it could significantly improve treatment outcomes for patients with neuroendocrine cancers — and the antagonist peptide DOTA-LM3 may offer even greater benefit.
The numbers in context
Compared 161Tb-DOTA-LM3 and 161Tb-DOTATATE against their 177Lu-labeled counterparts using CA20948 cell survival assays.
How the study worked
In vitro study using CA20948 neuroendocrine tumor cells. Clonogenic survival assays compared cell killing by 161Tb vs 177Lu with both DOTATATE and DOTA-LM3 peptides. Cell binding, internalization, and dissociation measured over 7 days. Monte Carlo simulations computed separate S values for each particle emission type. Survival curves fitted to linear or linear-quadratic models.
Who was studied
CA20948 neuroendocrine tumor cell line
What this study cannot tell us
In vitro study using a single cell line — tumor heterogeneity and microenvironment effects are not captured. 161Tb is not yet widely available for clinical use. Monte Carlo simulations assumed spherical cells, which may oversimplify actual cell geometry. The study didn't account for bystander effects or DNA repair capacity differences between cell types.
How to read the evidence
Preliminary evidence from rigorous in vitro dosimetry and cell survival studies. The physics and dosimetry are robust, but clinical translation of 161Tb-based PRRT requires in vivo validation.
When this study was published
Published in 2024, representing frontier research in next-generation radionuclide therapy for neuroendocrine tumors.
The bigger picture
Peptide receptor radionuclide therapy has transformed neuroendocrine cancer treatment. The shift from 177Lu to 161Tb could represent the next major advance, delivering more targeted radiation damage while using the same proven peptide-targeting platform. Combined with antagonist peptides that bind more receptors without internalizing, this could dramatically improve patient outcomes.
Questions still open
- Will 161Tb-DOTA-LM3's superior in vitro cell killing translate to better tumor control in animal models and clinical trials?
- Can 161Tb production be scaled sufficiently for clinical use, and at what cost compared to 177Lu?
Common questions
What is peptide receptor radionuclide therapy?
Why would terbium-161 be better than lutetium-177?
Read the original research
The Emission of Internal Conversion Electrons Rather Than Auger Electrons Increased the Nucleus-Absorbed Dose for 161Tb Compared with 177Lu with a Higher Dose Response for [161Tb]Tb-DOTA-LM3 Than for [161Tb]Tb-DOTATATE.
Journal of nuclear medicine : official publication, Society of Nuclear Medicine, 65(10), 1619-1625
Citation
Spoormans, Kaat; Struelens, Lara; Vermeulen, Koen; De Saint-Hubert, Marijke; Koole, Michel; Crabbé, Melissa. (2024). The Emission of Internal Conversion Electrons Rather Than Auger Electrons Increased the Nucleus-Absorbed Dose for 161Tb Compared with 177Lu with a Higher Dose Response for [161Tb]Tb-DOTA-LM3 Than for [161Tb]Tb-DOTATATE.. Journal of nuclear medicine : official publication, Society of Nuclear Medicine, 65(10), 1619-1625. https://doi.org/10.2967/jnumed.124.267873