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Radiation therapy for neuroendocrine cancer
Radiation therapy uses high-energy rays or particles to destroy cancer cells. Radiation may be used for neuroendocrine tumours and carcinomas:
- as the primary treatment to destroy cancer cells
- before surgery or chemotherapy to shrink a tumour (neoadjuvantneoadjuvantTreatment given to shrink a tumour before the first-line therapy (the first or standard treatment), which is usually surgery. radiation therapy)
- after surgery or chemotherapy to destroy cancer cells left behind and to reduce the risk of the cancer recurring (adjuvantadjuvantTreatment given in addition to the first-line therapy (the first or standard treatment) to help reduce the risk of a disease (such as cancer) coming back (recurring). radiation therapy)
- to relieve pain or to control the symptoms of advanced neuroendocrine cancer (palliative radiation therapy)
The amount of radiation given during treatment, and when and how it is given, will be different for each person.
Targeted radiation therapy
Targeted therapy means the treatment is delivered directly to the cancer cell (the target). Targeted radiation therapy is given by attaching radioactive material to an agent (usually a biological therapy drug) that binds to receptors on the cancer cell. This allows the radiation to be delivered directly to the cancer cell and limits its effects on normal cells.
Somatostatin is a peptide that binds to somatostatin receptors on neuroendocrine tumour cells. Somatostatin prevents the neuroendocrine cells from producing hormones by blocking these receptors. Because somatostatin has a short half-life (1–2 minutes), long-acting drugs with the same action (congeners) have been manufactured. Octreotide (Sandostatin) and lanreotide (Somatuline) are somatostatin congeners used to treat neuroendocrine tumours. For targeted radiotherapy, the drug is attached to radioactive tracers and injected into the person.
Targeted radiotherapy with radiolabelled somatostatin congeners is effective in treating some neuroendocrine cancers. It is also called peptide receptor radionuclide therapy (PRRT). In PRRT, a radioactive material (a radioactive isotope) is usually joined to octreotide. It travels throughout the body and attaches to receptors on cancer cells. The radiation from the radioactive isotope kills the cancer cells. Depending on how many cancer cells are destroyed, this treatment may relieve symptoms, increase survival and improve quality of life.
Some of these same radiolabelled somatostatin congeners are used to diagnose neuroendocrine tumours or carcinomas. They are given in lower doses when used for diagnosis.
Special safety precautions are taken after systemic radiation therapy. A person may also be given amino acids and potassium iodide to protect other organs (liver and thyroid) from the effects of the radioactive isotopes. Regular tests to check kidney function may be used to detect any kidney damage due to this type of radiation therapy.
Commonly used radioactive isotopes are:
- indium-111 pentetreotide
- I-131 metaiodobenzylguanidine (MIBG)
- Newer agents, such as somatostatin congeners labelled with lutetium-177, yttrium-90 or gallium, are not yet available in Canada. Many specialized centres in Europe have used somatostatin congeners with improved response. Nuclear medicine and healthcare specialists familiar with a person’s health and diagnosis can assess if these agents might be effective treatment options for their specific type and stage of neuroendocrine cancer.
External beam radiation therapy
External beam radiotherapy has limited use in the treatment of neuroendocrine carcinomas. It is used to treat brain and bone metastases.
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