Immunoscintigraphy is a radiological diagnostic procedure from the field of nuclear medicine. It involves the invasive application of so-called radioactively labeled antibodies via a patient’s vein, which then accumulate in sites of inflammation or tumor tissue.
What is immune scintigraphy?
Immunoscintigraphy invasively applies so-called radiolabeled antibodies through a patient’s vein, which then accumulate in sites of inflammation or in tumor tissue. Immunoscintigraphy uses artificial antibodies, i.e. these are not natural antibodies as they occur in the blood, but antibodies produced artificially for this purpose. Depending on the purpose, however, only individual antibody fragments are used, i.e. not the entire antibody. Both the fragment and the entire antibody can be additionally radioactively labeled. For this purpose, so-called tracers are used, which contain radioactive technetium, for example. However, other radioactive nuclides are also used in immunoscintigraphy. These antibodies, which are labeled in the nuclear medicine laboratory, are administered intravenously to the patient in a syringe. The bloodstream then rapidly distributes the antibodies to all body tissues and organs. Immunoscintigraphy is now used to selectively enrich these radiolabeled antibodies at suspected sites of inflammation, primary tumors or metastases. If the antibodies have accumulated on cancer cells or inflammatory cells, then these can be detected by the radioactive component using a so-called gamma camera.
Function, effect, and targets
Immunoscintigraphy was an experimental procedure for a long time, but then found its way into clinical medicine. Because of the complexity of the application, the possible side effects, and, last but not least, the high costs, the procedure is only used in a targeted manner for specific problems, especially in oncology. The indications, i.e. the areas of application of immune scintigraphy are oncological and inflammatory questions, for example in the diagnosis of primary chronic polyarthritis, PCP. However, immunoscintigraphy is mainly used in the diagnosis and follow-up of malignant tumors. In tumor diagnostics, immunoscintigraphy is based on the principle of monoclonal antibodies directed against very specific antigen structures on the surface of certain tumors. The binding of the respective labeled antibodies is therefore strictly specific and can so far only be limited to a few tumor types. Immunoscintigraphy is usually preceded by other oncological examinations. Whether the indication for the use of immune scintigraphy is actually given depends on histological, i.e. fine-tissue findings, as well as hormone tests of the blood. The main areas of application of immunoscintigraphy in oncology are certain forms of rectal cancer, sigmoid carcinoma, and non-Hodgkin’s lymphoma, a malignant disease of the lymphatic system. In non-Hodgkin’s lymphoma, immunoscintigraphy is considered very important for the course of therapy and for planning the radiation dose for therapy. In this type of tumor, radioimmunotherapy is generally not performed without waiting for the results of immunoscintigraphy. In inflammatory processes, immunoscintigraphy is used as a so-called inflammatory scintigraphy. The labeled antibodies can be enriched specifically or non-specifically. Specific enrichment uses monoclonal antigranulocyte antibodies that have been radiolabeled with technetium. The antibodies bind rapidly to granulocytes, a specific fraction of white blood cells, present in the bloodstream. These labeled granulocytes then migrate to the suspected site of inflammation and eventually accumulate there. Immunoscintigraphy is also used as a therapy for severe processes that cannot be influenced by medication. In this case, the immune scintigraphy acts as a radiopharmaceutical in the inflammatory focus; the radioactive destruction of the inflammatory focus stops the pathological process, even if only temporarily. In the so-called non-specific enrichment, no artificial antibodies are used, but human immunoglobulin is radioactively labeled with technetium. This process does not involve any specific binding to granulocytes.Immunoscintigraphy is approved in nuclear medicine for chronic recurrent inflammation and for the evaluation of prolonged febrile conditions. Once the radiolabeled antibodies have been prepared in all immunoscintigraphy applications, immediate venous administration is required due to the short half-life of technetium. After administration, the waiting time is between 1 to 72 hours until evaluation under the gamma camera, depending on the indication. A clear diagnostic chart is obtained, similar to thyroid scintigraphy, showing the accumulation of radiolabeled antibodies in the target area. The gamma camera continuously records the radioactive decay of the technetium with which the antibodies were previously labeled.
Risks, side effects, and hazards
Immunoscintigraphy carries some not inconsiderable risks, side effects, dangers and peculiarities. Absolute contraindication is gravidity, so the procedure must not be used during pregnancy. The lactation period, breastfeeding, is a relative contraindication. In order to safely prevent a risk to the infant, breastfeeding must be interrupted for at least 2 days. Repeat examinations are also a relative contraindication. An immunoscintigraphy should only be repeated after 3 months because of the comparatively high radiation exposure. Before each immunoscintigraphy, a precise risk-benefit assessment should be performed by radiologists and oncologists. This is because the risk of late malignancy in the form of carcinoma or leukemia is particularly increased by the application of radiolabeled antibodies. If malignant tumors occur years after application, they are not always directly associated with a previously performed immunoscintigraphy. If malignant neoplasms occur, the treating oncologist must be informed about previously performed diagnostic or therapeutic immunoscintigraphies, even if these occurred a very long time ago. As a side effect, allergic reactions to the administered radionuclide, including allergic shock, may also occur.
