ASN Report 2017

270 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 09  - Medical uses of ionising radiation 2.1.1 In vivo diagnosis This technique consists in examining an organ or a function of the organism with a specific radioactive substance – called a radiopharmaceutical – administered to a patient. The nature of the radiopharmaceutical depends on the studied organ or function. The radionuclide can be used directly or fixed to a carrier (molecule, hormone, antibody, etc.). Table 1, for example, presents some of the main radionuclides used in various investigations. The administered radioactive substance – often technetium- 99m – is localised in the organism using a specific detector and scintigraphy techniques. This detector, called a scintillation camera or gamma camera, consists of a crystal of sodium iodide (in the majority of cameras) coupled to a computerised acquisition and analysis system. This equipment produces images of the functioning of the explored tissues or organs. The physiological or physiopathological processes can be quantified. The majority of gamma cameras allow tomographic acquisitions, cross-sectional imaging and a three-dimensional reconstruction of the organs (Single-Photon Emission Tomography - SPECT). Fluorine-18, a positron-emitting radionuclide, is commonly used today, frequently in the form of a marked sugar, fluorodeoxyglucose, particularly in oncology. Its utilisation necessitates the use of a special camera (Positron Emission Tomography – PET camera). The principle of operation of PET cameras is the detection of the coincidence of the two photons emitted when the positron is annihilated in the matter near its point of emission. Other radiopharmaceuticals marked with other positron emitters, notably gallium-68, are starting to be used. Nuclear medicine enables functional images to be produced. It is therefore complementary to the purely morphological images obtained using the other imaging techniques. In order to make it easier to merge functional and morphological images, hybrid appliances have been developed: Positron- Emitting Tomography (PET) scanners are now systematically coupled with a CT scanner (PET-CT) and gamma-cameras are equipped with a CT scanner (SPECT-CT). The installation of semi-conductor cameras (CZT -Cadmium Zinc Telluride), which have very high detection sensitivity, is developing in particular in healthcare centres that perform a large number of examinations of the myocardial function. 2.1.2 In vitro diagnosis This is a medical biology technique for assaying certain compounds contained in biological fluid samples taken from the patient, such as hormones, tumour markers, etc., and it does not involve administering radionuclides to the patients. The technique uses assay methods based on immunological reactions (antigen-antibody reactions labelled with iodine-125), hence the name RIA (Radioimmunology Assay). The activities contained in the analysis kits designed for a series of assays do not exceed a few thousand becquerels (kBq). Radioimmunology is currently challenged by techniques which make no use of radioactivity, such as immuno- enzymology and chemiluminescence. A few techniques use other radionuclides such as tritium or carbon-14. Here again the activity levels involved are of the order of the kBq. 2.1.3 Internal targeted radiotherapy Internal Targeted Radiotherapy (ITR) aims to administer a radiopharmaceutical emitting ionising radiation which will deliver a high dose to a target organ for curative or remedial TYPE OF EXAMINATION RADIONUCLIDES USED Thyroid metabolism Iodine-123, Technetium-99m Myocardial perfusion Thallium-201, Technetium-99m, Rubidium-82 Lung perfusion Technetium-99m Lung ventilation Technetium-99m, Krypton-81m, Osteo-articular process Technetium-99m, Fluorine-18 Renal exploration Technetium-99m Oncology - search for metastasis Technetium-99m, Fluorine-18, Gallium-68 Neurology Technetium-99m, Fluorine-18 TABLE 1: Some of the main radionuclides used in the various in vivo nuclear medicine examinations POSITRON EMISSION TOMOGRAPHY CAMERAS COUPLED TO A COMPUTED TOMOGRAPHY SCANNER (PET-CT) SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY (SPECT) CAMERAS HYBRID CAMERAS COMBINING A COMPUTED TOMOGRAPHY SCANNER WITH SPECT-CT PET CAMERAS COUPLED WITH AN MRI MACHINE 145 200 250 3 and 2 at project stage TABLE 2: Number and type of tomography cameras used in nuclear medicine (2017)