Nuclear medicines constitute a special class within medicine, utilizing radioactive substances (radionuclides) for the diagnosis and treatment of various conditions, including cancer. The combination of diagnosis and treatment is also referred to as theranostics, and this unique combination enables concrete steps to be taken in the areas of personalized treatments, patient selection, and minimizing side effects. Nuclear medicines come in various forms, each with its own unique properties.

Targeted radionuclide therapy (TRT) is the largest class of nuclear medicines. In this approach, a radionuclide is linked to a target molecule that binds to cancer cells or structures close to the cancer cells. During diagnosis, the target molecule can be linked to a radionuclide that is particularly suitable for imaging, to make a diagnosis and determine a treatment strategy. During therapy, the same target molecule can be linked to a different radionuclide to treat the tumor in a targeted manner. A well-known example of this is the use of fluorine-18 PSMA for the diagnosis of prostate cancer and targeted treatment with lutetium-177 PSMA. The major advantage of TRT is that it works with great precision, thereby sparing healthy tissues as much as possible and preventing side effects. This makes the therapy particularly suitable for hard-to-reach or metastatic tumors.

Sometimes the radionuclide is not bound to a target molecule but finds its way to the treatment site on its own. This is the case, for example, with the longest-standing nuclear treatment: radioactive iodine for thyroid disorders. We often refer to this application as TRT as well.
In local radionuclide therapy, radioactive material is delivered directly to the tumor. This can be done by placing a radioactive source during surgery (brachytherapy) or by injecting the source through a blood vessel leading to the tumor (radioembolization). This treatment is often considered a medical device because the material remains in the body after the radioactivity has faded. Because the radiation in local radionuclide therapy is concentrated near the tumor, there are usually few side effects, even though a high dose of radiation is delivered locally. However, the treatment is limited to one or a few easily accessible sites and is not suitable for metastatic disease.

Depending on the type of tumor, different radionuclides, target molecules, and routes of administration can be selected to determine the most appropriate treatment. For example, the type of radiation (alpha, beta, and/or gamma, with each type having a different penetration depth in tissue), the half-life or dose rate (how quickly the radionuclide decays, or how long it takes for the radiation to be emitted), and the administered activity (the amount of radioactive agent administered in becquerels) can be tailored to the type of tumor and the individual patient. In recent years, research into such effective and minimally invasive nuclear medicines has increased significantly, and this field of research is rapidly evolving for various tumor types.