Radionuclide therapy
| Radionuclide therapy | |
|---|---|
| ICD-9-CM | 92.28 |
Radionuclide therapy (RNT, also known as unsealed source radiotherapy or molecular radiotherapy) uses radioactive substances called radiopharmaceuticals to treat medical conditions, particularly cancer. These are introduced into the body by various means (injection or ingestion are the two most commonplace) and localise to specific locations, organs or tissues depending on their properties and administration routes. This includes anything from a simple compound such as sodium iodide that locates to the thyroid via trapping the iodide ion, to complex biopharmaceuticals such as recombinant antibodies which are attached to radionuclides and seek out specific antigens on cell surfaces.
This is a type of targeted therapy which uses the physical, chemical and biological properties of the radiopharmaceutical to target areas of the body for radiation treatment. The related diagnostic modality of nuclear medicine employs the same principles but uses different types or quantities of radiopharmaceuticals in order to image or analyse functional systems within the patient. The mechanism of action of radionuclide therapy is the delivery of ioninzing radiation to the target tissue, inducing cellular oxidative stress and DNA damage, resulting in cell death. The choice of the radionuclide depends on its emission pattern (which determine its use in therapy and/or diagnosis), its physical half-life, and the pharmakokinetics of the targeting probe . Radionuclides employed for therapeutic purposes range from β-particle emitters to α-particle emitters.
β-particle emitters release low-energy electrons with a long tissue range of up to 12 mm, which allow them be used to treat larger tumors. These are the most employed radionuclides given their availability and in some cases, the co-emission of γ-radiation photons which enables imaging using SPECT/CT imaging . β-emitters commonly used in oncology include Lutetium-177, yttrium-90 or Iodine-131. Lutetium-177 combines therapeutic electron emissions with γ-radiation emission compatible with SPECT/CT imaging cameras, integrating therapy and diagnostics in the same targeting probe (Theranostics) when using the same radionuclide . Some other β-emitters co-emit internal conversion and Auger electrons, such as Terbium-161, which delivers additional ionization at shorter distances (under 500 nm) . α-particle emitters on the other hand, release heavy particles with a short tissue range of up to 100 μm, depositing high-energy radiation. The deposited energy per length of α-particle emitters is 400 times larger than β-particle emitters, which yields more effective DNA damage, with irreparable double-strand DNA breaks . α-emitters like Actinium-225, Lead-212, Astatine-211 or Thorium-227 have gained attention for clinical implementation in recent years due to their emission properties. Radionuclides with such short distance emissions have been shown to be effective mainly in treating micrometastasis.
RNT contrasts with sealed-source therapy (brachytherapy) where the radionuclide remains in a capsule or metal wire during treatment and needs to be physically placed precisely at the treatment position.
When the radionuclides are ligands (such as with Lutathera and Pluvicto), the technique is also known as radioligand therapy.