Summary (10 sec read)
Terbium-161 is a promising radioisotope in nuclear medicine, offering similar properties to Lutetium-177 but with added benefits. It emits Auger electrons for enhanced cell kill, delivers 40% more radiation per unit, and reduces toxicity risk—making it a potential bridge between beta and alpha therapies for more effective, targeted cancer treatment.
Terbium is emerging as a very exciting radioisotope in the field of nuclear medicine, primarily because it closely mirrors the characteristics of Lutetium-177. Both have comparable physical properties — for example, the half-life of Lutetium is about 6.6 days, while Terbium’s is approximately 6.8 days. Their beta emission energies are also similar, making Terbium an excellent candidate for targeted radioligand therapy.
What truly sets Terbium apart, however, is its additional emission of Auger electrons and conversion electrons. These are extremely small, highly energetic particles with minimal tissue penetration, meaning they deposit energy very locally. This feature allows Terbium to specifically target and destroy residual microscopic cancer cells that are often left behind on tumor surfaces — cells that may escape the deeper-penetrating beta emissions of Lutetium and lead to future recurrence.
One of the most compelling theoretical advantages of Terbium is the possibility of reducing recurrence rates by eliminating these single tumor cells more effectively.
Moreover, Terbium has been shown to deliver approximately 40% more radiation dose per unit of radioisotope injected. This means that compared to Lutetium, we could administer 30–40% less Terbium to achieve the same radiation dose to the tumor, thereby potentially reducing systemic toxicity. This reduction is especially important because every unit of radioisotope carries some inherent risk — particularly to the kidneys and bone marrow — even if it’s not immediately clinically apparent.
Conversely, if we use the same quantity of Terbium as Lutetium, we could deliver significantly more radiation to the tumor site — and as we’ve seen with alpha emitters, a higher, more focused radiation dose tends to correspond with better tumor response.
This positions Terbium as a potential ‘bridge’ between beta emitters like Lutetium and more powerful alpha emitters such as Actinium-225. While alpha particles provide extremely high energy with excellent therapeutic effects, they also come with higher toxicity risks. Terbium, by contrast, may offer enhanced efficacy without the same level of adverse effects.
Another key advantage is Terbium’s compatibility with existing ligands. Just like Lutetium, it can be labeled with PSMA for prostate cancer, DOTATATE for neuroendocrine tumors, and even newer agents like FAPI. This allows us to extend all the known benefits of targeted radioligand therapy — now with the added potency of Terbium’s Auger electron emission.
While more clinical evidence is needed to confirm all these hypotheses, the current understanding strongly supports Terbium-161 as a promising, next-generation isotope for targeted cancer treatment.