A Radioactive Glowing Marker for Targeted Therapy express
The radioactive isotope terbium-149 acts like a tiny homing bomb: it latches onto cancer cells and detonates with alpha particles that destroy the tumor from within, barely touching healthy tissue. But this bomb has a quirk: it also glows with positrons, and that glow can be captured by a special camera. The catch is that the glow is faint and accompanied by extra flashes that muddy the picture.
Researchers took a plastic body phantom with spheres of various sizes mimicking tumors, filled it with a terbium-149 solution, and scanned it on a modern PET/CT scanner with a long field of view. Even when they reduced the activity to a tenth of the original, the images remained sharp, and the accuracy of dose measurement stayed within the standards used for conventional fluorine-18. A special software setting that accounts for the extra flashes helped yield reliable numbers.
This approach paves the way for personalized dosimetry: a doctor could see how much of the drug actually accumulated in the tumor and calculate in advance the radiation dose the patient will receive. It's like a bomb disposal expert seeing on a screen exactly where the explosives are placed before pressing the button.
Original abstract
as written by the authors arXiv:2604.02053
Introduction: Terbium-149 ($$^{149}$$Tb) is a promising radionuclide for targeted $$\alpha$$ therapy that has a non-zero branching ratio (BR) for positron decay. However, its relatively low positron branching fraction and multiple prompt $$\gamma$$ emissions may challenge quantitative imaging. This study evaluates, for the first time, the imaging performance and quantitative accuracy of $$^{149}$$Tb using a clinical long axial field-of-view (LAFOV) PET/CT system. Methods: Quantitative accuracy of $$^{149}$$Tb was assessed with a NEMA IEC body phantom, which was filled with about 45 MBq $$^{149}$$Tb and a sphere-to-background ration of 10:1. The phantom was scanned for 20 min and shorter scan times and lower activities were simulated. Recovery coefficients, coefficient of variation, and lung residual error were evaluated for different reconstruction settings and compared to the EARL standard 2 for $$^{18}$$F. Results: High-quality PET images of $$^{149}$$Tb were obtained, even with a simulated total activity of 4.5 MBq. The 20 min and full activity scan yielded a mean recovery coefficient $$RC_\textit{mean}$$ of $$0.55$$, $$0.69$$, $$0.73$$, $$0.76$$, $$0.79$$, and $$0.81$$ for the six phantom spheres. Despite the low count statistics, the coefficient of variation stays mostly below $$15\,\%$$. Relative scatter correction combined with prompt $$\gamma$$ modeling provided robust quantification. Conclusion: $$^{149}$$Tb can be imaged using a commercial LAFOV PET/CT with a quantitative accuracy comparable to the EARL standard 2 for $$^{18}$$F. These findings demonstrate the feasibility of PET-based treatment verification and dosimetry for targeted $$\alpha$$ therapy with $$^{149}$$Tb.
Terbium-149 is named after the Swedish village of Ytterby, where a mineral containing rare earth elements was first found — yttrium, erbium, and ytterbium also get their names from this same village.