Radionuclide therapy is use of a radioactive substance that is injected or ingested into the body. Once given, the substance goes preferentially to the area of cancer. It then emits radiation locally with the aim to destroy cancer cells in the area. The radionuclides used for such therapies are radioisotopes which emit different types of radiation such as alpha particles, beta particles or gamma radiation. These particles have different properties which affect how the treatments work.
There are many radionuclide therapies that are used in cancer and these are listed here briefly. This is an expanding field with newer treatments coming up more often now. It is a type of treatment that is used for some types of cancers. It is not a general treatment for all cancers such as radiotherapy or chemotherapy.
Iodine 131 (I 131)
Iodine 131 is an isotope of Iodine that is used to treat thyroid cancer. The thyroid gland needs iodine to function normally and is the only organ in the body which needs a significant amount of iodine. So, in thyroid cancer (papillary or follicular), a radiation emitting isotope of Iodine is given in the form of a capsule swallowed by the patient. This is taken up by the cancer cells and the radioisotope emits this radiation in the area, killing of the cancer cells that may be present in the body. This treatment is given after surgery for thyroid gland. As it is selective taken by the thyroid cancer cells and few other normal cells in the body, the side effects of treatment are mild.
Peptide receptor radionuclide therapy (PRRT)
This type of radionuclide therapy is used in the treatment of neuroendocrine cancers. Neuroendocrine cancers have somatostatin receptors on their cells. In these conditions, the radionuclide is combined with a somatostatin analogue. The analogue helps attach the drug to the cancer cell and the radionuclide produces the radiation effect on the cancer cell. Commonly used radionuclides are Lutetium Lu-177 dotatate and Yttrium-90 Dotatoc.
Yttrium 90 is an isotope of Yttrium and is used in the treatment of tumours in the liver. It can be used in primary liver cancer (Hepatocellular carcinoma) or in patients with other cancers that have spread to the liver (colon or rectal cancer). This isotope is injected into the blood vessels near the tumour and it delivers radiation near the tumour to control it.
Ibritumomab tiuxetan (Zevalin) Yttrium 90
This drug is used to treat a lymphoma that has released after initial treatment. Ibritumomab is an anti cd20 monoclonal antibody that acts against lymphoma and attaches to the lymphoma cells. It is given as an injection and the Yttrium 90 delivers local radiation near the lymphoma cells.
Iodine 131 meta-iodobenzylguanidine is a molecule used to treat neuroendocrine tumours such as pheochromocytoma, paraganglioma and neuroblastomas. MIBG is taken up by these tumours and the I 131 delivers the radiation to the cancer cells.
Radionuclide therapy can be used to treat stage 4 prostate cancers after all standard treatments have been used. Prostate cancer commonly spreads into the bones and causes bone pain.
Samarium-153 and Strontium-89 are radioactive isotopes which are taken up in the bones to help control the cancer and improve pain. Their role is mainly to control symptoms.
Radium-223 is an isotope of Radium which has been shown to be beneficial in improving survival in patients with prostate cancer with bone metastases. This given as an injection.
Lutetium-177 PSMA is a molecule that contains a Lutetium-177 radioisotope combined with PSMA which is prostate specific membrane antigen. This type of combination is also known as radioligand therapy (RLT). PSMA is present on the surface of prostate cancer cells and helps the radioisotope deliver treatment locally.
Side effects of Radionuclide therapy
Treatment with radionuclide therapy can be associated with side effects and these are specific to the cancer and the type of treatment used. Usually, the side effects are mild but can include serious side effects also. The doctor doing the treatment will explain the potential side effects of treatment.
As these drugs are radioactive substances, precautions need to be taken by patients and staff to prevent radiation exposure to others. This may involve isolation of the patient after treatment and this depends on the treatment and dose used. For some treatments, the patient may have to stay in hospital for a few days after treatment before going home.