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Application of ionising radiation in healthcare is basic and routine in contemporary medicine. Benefits to patients from such application have been established beyond doubt.<ref name="Pub105">[[ICRP Publication 105]] Radiological Protection in Medicine. Ann. ICRP 37(6), 2007.</ref> It is difficult to imagine a healthcare system without modern diagnostic imaging and image-guided interventional procedures. A survey of policy leaders in internal medicine rated computed tomography (CT) imaging as one of the main healthcare innovations in the 20th century<ref>Fuchs and Sox, 2001 [https://www.ncbi.nlm.nih.gov/pubmed/11558715]</ref>. The applications of ionising radiation in healthcare include the following topics.
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[[file:figure 1.1.3.jpg|200px|left|thumb|'''Figure 1:''' Example of plain film radiography''']][[file:Brain-Computed tomography.jpg|200px|thumb|'''Figure 2:''' Example of brain Computed tomography ''' ([https://www.researchgate.net/publication/5822266])]][[file:Pet_CT.jpg|200px|thumb|'''Figure 3:''' Example of true positive metastatic lesions detected by 18F-FDG PET/CT restaging (''' Courtesy: of Eur. J. Nucl. Med. Mol. Imaging, 45: 1742/CC By 4.0)]]
Diagnostic radiology, the imaging modalities using ionizing radiation, produces images of anatomical internal structures of human organs and physiological (functional) biological systems and helps significantly improve patient management and care in screening and diagnosis, assessing treatment response, predicting prognosis, and detecting disease recurrence. Modern diagnostic radiology assures faster, more precise diagnosis and enables monitoring of a large proportion of diseases. It has been estimated that in about one half of all cases, radiological procedures (conventional radiography, fluoroscopy, computed tomography) have a substantial impact on the speed of diagnosis and in a large fraction of cases they are of decisive importance in guiding patient management and therapy.
==Interventional Procedures==
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[[file:PTA.jpg|200px|thumb|left|'''Figure 4:''' Percutaneous Transluminal Angioplasty (PTA) of the superficial femoral artery (SFA). Left image: subtotal calcified occlusion a) with many collaterals b); Right image: good patency after ballon PTA''']]
Interventional procedures using ionising radiation have revolutionised medicine in the past few decades for therapy and palliation, resulting in more patients being offered treatments that would not have been possible before with more invasive open surgery. The vast majority of interventional procedures are performed as “minimal invasive percutaneous therapies”.
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[[file:Figure 1.4.1.jpg|200px|thumb|'''Figure 5:''' A TrueBEAM Radiotherapy System by Varian Medical Systems (''' Photo credit: courtesy of Dr. W. Small, Loyola University Chicago)]]
Radiation therapy utilizes ionizing radiation to treat malignant and benign diseases. It has become a standard of care for treating many types of cancer. Current medical practice uses radiation therapy in about half of all newly diagnosed cancer cases. Radiation therapy works by exploiting radiobiological differences between cancer and normal cells/tissues, and by depositing radiation dose in cancer tumours while keeping doses to surrounding normal tissues below damaging thresholds as much as possible.
Radiation therapy is used as a primary, curative treatment, as a palliative treatment, and/or as adjunctive therapy. It can be used pre-operatively or post-operatively, and in combination with chemotherapy, biologic agents, and hormonal agents. The radiation dose prescribed to achieve tumour control is often limited by the radiosensitivity of normal tissues, which are located around the tumour, and thus may result in early and late adverse side effects. Some adverse effects are unavoidable and often resolve spontaneously or with treatment. Serious adverse effects may occur and result from the proximity of sensitive normal tissues to the treatment area. However, such adverse side effects do not undermine the purpose of radiation therapy. Appropriate use of radiation therapy saves millions of lives every year. Even if only palliative treatment is possible, the therapy reduces suffering substantially. There are also a few non-malignant diseases whose treatment by radiation is a method of choice. Note that palliative radiotherapy and radiotherapy of non-malignant diseases uses much lower doses, generally not inducing any acute side effects.
Radiation therapy has benefited greatly from technological advances over the past two decades, resulting in a wide variety of available delivery methods: Intensity-modulated radiation therapy (IMRT) utilizing techniques to quantify the critical normal tissue doses; Image-guided radiotherapy (IGRT) utilizing real-time imaging for treatment localization during radiotherapy; Stereotactic radiosurgery (SRS) delivering of a large dose per fraction to treat focal brain lesions and its extension, stereotactic body radiation therapy (SBRT), to treat focal lesions in the lung, spine, liver, pancreas, prostate and all parts of the body; Particle beam radiotherapy utilizing protons, neutrons or other heavy particles; Brachytherapy placing sealed radioactive sources near the tumor; Intraoperative radiotherapy (IORT) delivering to the surgical bed after removal of the tumor or to the tumor itself at the time of surgery; Unsealed sources delivering a radiopharmaceutical orally or parenterally; and Hyperthermia adding of heat to radiotherapy.
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{{#evt:service=youtube|id=https://youtu.be/0USC0C6qG9w|dimensions=500|container=frame|alignment=right|description=Video courtesy of the International Atomic Energy Agency}}
[[file:Bone_Scan_2.jpg|left|200px|thumb|'''Figure 6:''' Example of an abnormal whole-body bone scan. Illustrates an abnormal bone scan in a patient which is marked with arrows. Source: ''' Images Courtesy of Health Sciences Centre - Winnipeg, Manitoba.]]
Nuclear medicine uses radioactive substances, called radiopharmaceuticals, in the diagnosis and treatment of a range of diseases. These substances are chosen or especially developed to be taken up predominantly by one organ or one type of cell in the body. Nuclear medicine offers unique diagnostic information in oncology, cardiology, endocrinology, neurology, nephrology, urology and other areas. Such information is not obtainable, or obtainable only with less accuracy, by other modalities. For nuclear medicine diagnostic procedures, trace amounts of radiopharmaceuticals are administered to patients through injection into veins (intravenous), skin (intradermal) or tissues (intraparenchymal) as well as breathing in (inhalation) or eating/drinking (ingestion). After intake, the function, or physiology, of various tissues, organs or organ systems can be demonstrated. For example, in cancer patients, nuclear medicine imaging can be used for diagnosis (i.e. is a cancer present), staging (i.e. how far has it spread), assessment of response to therapy or of possible disease recurrence. Nuclear medicine cameras are now commonly combined with a CT unit (e.g. hybrid SPECT/CT and PET/CT) which allows precise anatomic localisation of pathology.
[[file:SPECT_CT_gamma.jpg|200px|thumb|'''Figure 7:''' Example of a SPECT/CT gamma camera (Source: © 2018 Siemens Healthcare GmbH. ''' All Rights Reserved. Product photo provided courtesy of Siemens Healthcare GmbH) ]]
Nuclear medicine procedures for treatment are non-invasive and present no risk of direct complications to patients, but limited to several well-established situations where killing hyperfunctioning or malignant cells is important (for example hyperthyroidism, cancer of the thyroid, degenerative and inflammatory diseases of joints, palliative treatment of metastases to the skeleton). In addition, there are many studies showing significant potential for radio-labelled antibodies and receptor-avid peptides to be used in the treatment of several malignancies.
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[[file:mousescan.jpg|200px|thumb|'''FDG PET image of a mouse''' Images Courtesy University of Manitoba Small Animal and Materials Imaging Core Facility]]
Ionising radiation is widely used in biomedical research. Such research is normally carried out in the laboratory and using different animal models. Research on normal tissue radiobiology aims at the investigation of the pathophysiological mechanisms and the consequences of ionising radiation. Pre-clinical in vivo studies in experimental animals largely focus on the characterisation of the pathophysiology of normal tissue reactions, the identification of potential biomarkers or the establishment of assays for predicting normal tissue toxicity of radiotherapy. Establishment of tumor xenograft models, involving implantation of human patient-derived tumors into immunodeficient animals, is a valuable research tool to investigate the biological effects of ionizing radiation on the disease mechanism of cancer.
{{#evt:service=youtube|id=https://youtu.be/V6VZspB0pAQ|dimensions=500|container=frame|alignment=right|description=Video courtesy of the International Atomic Energy Agency}}
[[file:LINAC_dog.jpg|200px|left|thumb|'''Figure 8:''' Linear accelerator treatment of a dog with a brain tumour (''' Photo courtesy of J. Benoit)]]
Just as in human medicine, the use of ionising radiation in veterinary care serves to provide or assist in providing a diagnosis, to guide an interventional procedure or to provide a direct radiation-induced therapeutic benefit. The use of diagnostic radiology is widespread in veterinary care, in veterinary clinics or in private practices. Smaller companion animals are typically radiographed at the practice or clinic, whereas larger animals may also be radiographed at farms, zoos, or at riding and selling stables. Film-screen radiography is being replaced more and more by digital imaging techniques; CT and CBCT scanning have become routinely available in larger animal clinics. Fluoroscopically guided interventional procedures are also used in veterinary medicine. In these procedures, the radiation serves to provide dynamic, real-time images. The images will guide the anatomically correct delivery of treatments and will often allow real-time visualization of the results of the intervention.
[[file:Portable_PET_1.6.jpg|200px|thumb|'''Figure 9:''' A portable PET scanner being used for diagnosis of the left hind-leg of a horse (''' Photo courtesy of Dr. Spriet, UC Davis Veterinary Medicine, USA)]]
In therapeutic nuclear medicine procedures a much higher dose (“activity”) of radioactive substances is administered to the animal. The radiation dose delivered to the targeted tissue or organ then becomes so high that cells within this tissue or organ are inhibited in their proliferation or even eliminated. If a cancer is being targeted, complete elimination of the cancerous growth is the desired objective. But in treating other diseases such as hyper functioning of the thyroid gland or inflammation of the joints, inhibition or partial destruction may be sufficient for achieving the desired clinical goal. In the more classical radiotherapy, radiation generated outside the animal patient is also used to eliminate tissues that are undesired. Most often this will be used for treating animal patients affected by cancer.
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==References==
