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.