Theranostics

A Theranostics approach to nuclear medicine combines diagnostic imaging and therapy using a radioactive drug to diagnose and a second radioactive drug to deliver therapy to treat the primary tumour site.  However, the same radiopharmaceutical can be used in some cases, such as Zevalin- based on monoclonal antibody radioimmunotherapy treatment – for non-Hodgkin’s lymphoma.  

The drug uses the monoclonal mouse IgG1 antibody ibritumomab conjugated with tiuxetan. The chelator holds yttrium-90 for therapy or indium-111 for diagnostic imaging. Radioiodine was the first theranostic radiopharmaceutical used in nuclear medicine for the treatment and imaging of thyroid diseases.  

In the case of radioiodine therapy, the radioisotope iodine-131, which is a gamma and beta emitter, or the gamma emitter iodine-123, can be directly mediated by the sodium-iodide symporter in thyroid cells.  Theranostics uses a variety of radionuclides; for example, iodine-131 and lutetium-177 are both gamma and beta emitters and are used for imaging and therapy.

Theranostics can be useful for assessing the potential response and toxicity during treatment and can be applied to monitoring the course of therapy. Nuclear imaging utilises gamma and positron emitters (β+ +). Gamma emitters, such as technetium-99m or iodine-123, can be located using gamma cameras (planar imaging) or SPECT imaging. 

However, better resolution can be accomplished via PET imaging using positron emitters, such as gallium-68 and fluorine-18.  Most therapeutic radiopharmaceuticals are labelled with beta-emitting isotopes (β−), and tissue penetration of these particles is proportional to the energy of the radioisotopes. 

Beta particles have a potential cytocidal effect and only penetrate the tissue by a few millimetres, sparing the surrounding healthy tissue. The most commonly used beta emitters in routine nuclear oncology include lutetium-177 and yttrium-90. 

Nuclear-targeted therapies are vital, especially in patients with advanced neuroendocrine and gastroenteropancreatic tumours, including neuroblastoma.

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