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Some biomolecules, like monoclonal antibodies or specific peptides, can selectively target particular cancer cells; they will find these cells, even if spread around the body, and bind to them.

If an alpha-emitting radionuclide is attached to such a tumour specific carrier, the alpha particle produced during its radioactive decay can kill one or a few targeted cancer cells along its trajectory.


The typical radio-immunoconjugate has 3 components:
- a tumour selective carrier molecule, such as an monoclonal antibody or a peptide
- an alpha-emitter (typically Bi-213 or Ac-225)
- a chelator linking the two.

Alpha particles have a high linear energy transfer (LET) and short range in tissue: they release their high energy, and therefore create damage, over just a few cell diameters. They can therefore destroy tumour cells with minimal damage to surrounding healthy tissue. Cell killing essentially results from ionisation and rupture of chemical bonds due to the transfer of the alpha particle's kinetic energy.

Trajectory, range and energy deposit (ionisation density) of a beta particle (from Y-90, top), and
an alpha particle (from Bi-213, bottom), superimposed on a microscopic image of cells.

Due to the short range of alpha radiation in human tissue, targeted alpha therapy seems particularly attractive for disseminated cancers, like blood-borne and micro-metastatic tumours, or residual tumour cells that may remain after surgery, external beam radiotherapy or chemotherapy.