Why Actinium-225

Actinium-225 (²²⁵Ac) is an alpha particle-emitting radionuclide that generates four net alpha particle isotopes in its decay chain, culminating in stable Bismuth-209.

This characteristic makes Actinium-225 an alpha particle in-vivo generator, which is highly beneficial for targeted alpha therapy (TAT) as it allows for multiple instances of cell damage within a localized area, increasing the likelihood of effective treatment.

High Linear Energy Transfer & Range

The efficacy of Actinium-225 in TAT is attributed to its high linear energy transfer (LET). High LET radiation like alpha particles causes dense ionization along their tracks, leading to significant biological damage to targeted cells. This property is particularly advantageous in cancer treatment, where the goal is to maximize damage to cancer cells while minimizing the impact on surrounding healthy tissue.

Alpha particles exhibit a higher interaction frequency with matter compared to beta particles. Consequently, they more effectively ionize their surroundings. However, this increased potency comes at the cost of a shorter range, as alpha particles rapidly lose their initial energy due to frequent interactions. As a result, alpha particles cause greater damage to DNA and cells within a smaller volume when compared to beta particles.

Due to the limited range of alpha particles, which typically extends only a few cell diameters, TAT allows more precise irradiation. This limited range ensures that the cytotoxic effects are confined to the immediate vicinity of the targeted cancer cells, reducing the risk of collateral damage to adjacent healthy cells.