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Applications of Nuclear Techniques in Medicine


» Diagnostic Methods | Treatment of Disease | Disease Management | Future Plans and Developments

Nuclear energy saves lives. As one of the tools used in the human health area, nuclear energy can be harnessed and used in a variety of techniques to prevent, diagnose, and treat disease.

Techniques using nuclear energy in medical sciences have the unique ability to show bodily functions across time - as a film shows picture frames one after the other - quickly and accurately. The significance of this advantage is clear when one realizes that one out of every three patients attending a hospital in an industrialized nation benefits from some type of nuclear procedure.

The International Atomic Energy Agency (IAEA) and the World Health Organization (WHO) play a key role in the development and transfer of nuclear techniques, experience, and technical know-how to Member States - particularly developing countries.

Diagnostic Methods

Worldwide, more than half of the total number of cancer cases are in developing countries, the WHO estimates. Some 75% of these patients have been found to be incurable at the time of diagnosis. These statistics are changing due to two distinct diagnostic techniques - in vivo and in vitro. These methods determine the presence of a disease and the extent to which it has invaded the body and can help to determine the best means of treatment.

In Vivo Techniques

In vivo diagnostic techniques are based on an approach called the "tracer" principle. A radionuclide - in a carefully chosen chemical form and duration of being radioactive called a radiopharmaceutical - is administered to the patient to trace a specific physiological phenomenon by means of a special detector, often a gamma camera, placed outside the body. The radiopharmaceutical can be designed to seek out only desired tissues or organs, such as the lungs. By directing radiation only where it is needed, rather than randomly, modern techniques increase the health benefits available through nuclear applications.

Some 100-300 available radiopharmaceuticals mostly organic in nature and labeled with artificial radionuclides, such as indium-111 and gallium-67, are used to study organs and tissues without disturbing them. Nuclear diagnostic methods expose the patient to a small radiation dose. This is minimized further through the use of more short-lived radioisotopes, such as technetium-99m, which decay to stable form within hours.

The radiopharmaceutical is administered to the patient, usually by intravenous injection, oral ingestion, or inhalation. Through the use of a special detecting device, a gamma camera, it is observed as it travels throughout the body where it is specifically concentrated in a given tissue or organ. A gamma camera detects photons escaping the body, creating a two-dimensional image with the help of a computer and a video display unit. These images depict the regional quality of a specific function in a given organ. This process is called planar imaging or static scintigraphy.

These images, when received in a fast successive fashion, create a dynamic study of the radiopharmaceutical behavior, revealing such detailed functional information as the emptying of the stomach, the breathing process in the lungs, or the pumping activity of the heart.

Common Radionuclides and Their Uses

Iosotope Use Half-life*
99mTc Heart studies 6h
123I Thyroid studies 13h
201Tl Myocardial studies 78h
11C Brain imaging 20m
111In Brain studies 67h
67Ga Tumour studies 78H
81mKr Lung studies 13s
13N Heart studies 10m
15O Oxygen studies 2m
18F Epilepsy 110m

* h=hours; m=minutes; s=seconds

Such procedures may, like an X-ray, provide a picture of some particular body organ or part of it. The essential difference is that in nuclear medicine, the picture obtained provides a measure of the activity of a specific physiological or biochemical function in the body, while an X-ray image depicts anatomical details.

With the increased power of modern computers, clinical images can be acquired at multiple angels, creating a replica of the body's cross-section, a technique called computerized tomography (CT). The two most advanced forms using radionuclides are single-photon emission computed tomography (SPECT) and position emission tomography (PET).

SPECT uses a rotating gamma camera to obtain images from multiple angles of the distribution of a conventional gamma emitting radiopharmaceutical within an organ. This technique is particularly valuable because of its unique ability to locate the exact position of a physiological abnormality in the body through a series of computer-generated bidimensional slices of the organ, from which three-dimensional pictures of the organ can be reconstructed.

PET, valuable in the detection and management of cancer, employs one or several rings of stationary detectors around the patient's body to detect very strong diverging gamma-rays (511 keV) produced by the interactions of positrons (emitted by a previously administered radionuclide) with the free electrons within the body. This information is then processed to create body slices similar to those obtained by SPECT. PET has the unique ability to depict regional biochemical processes within the body and can demonstrate the biochemical foundation of neurological disorders and mental diseases.

In Vitro Techniques

The second method of diagnosis, in vitro, allows clinical diagnosis without the patient being exposed to radiation. In fact, the patient need not even be present. A blood sample taken from the patient is sent to the laboratory and examined through nuclear techniques such as radioimmunoassay (RIA), or immunoradiometric assay. (IRMA).

These tests measure precisely previous and current exposure to infection by assessing antibodies. RIA is also used to measure substances such as hormones, vitamins, and drugs in the body fluids in the detection of nutritional and endocrinological disorders and to track bacterial and parasitical infections such as tuberculosis and malaria. Supported through IAEA co-ordinated research programmes, some 500 hospitals, universities, and laboratories in the developing world alone are engaged in RIA on some scale and the numbers are increasingly annually.

Another application of RIA and IRMA techniques includes the detection of tumour markers, which are specific substances secreted by many, but not all, tumours and can indicate the presence of malignancy. Nearly two dozen tumours markers are available. Despite the increased accuracy, as well as cost and convenience factors, tumour markers remain complementary to other diagnostic procedures in the detection of cancer during its early stages, but they are especially valuable in monitoring the progress of disease and the effects of treatment.

Treatment of Disease

Radiation is widely used in the treatment of diseases, such as hyperthyroidism and cancer. To control the disease, or to prevent recurrence through spreading of loose cancerous cells which can lead to secondary cancer, all malignant cells in a tumour must be completely destroyed.

Radiotherapy accomplishes this by focusing radiation to a specific tumour, most often using cobalt-60 gamma rays, or high-LET (linear energy transfer) systems, as energy sources.

The radiation source can have either no contact with the tumour, an external treatment technique called teletherapy, or can be in direct or immediate contact with the tumour, a technique called brachytherapy. Brachytherapy, applied in special cancer types - such as cancer of the cervix of the head and neck - provides protection against radiation for delicate, healthy organs or tissues by directing radiation only to a specific site. Brachytherapy can not only treat but, in particular cases, can also cure many patients.

Being effective, simple to operate, and relatively inexpensive, brachytherapy is helping to save the lives of hundreds of cervical cancer patients in Egypt alone through work supported by the IAEA, the WHO, and the Government of Italy.

Only recently developed, another procedure using radiolabelled monoclonal antibodies is valuable in the treatment of cancer. Monoclonal antibodies, which are disease fighting proteins, seek out and bind to a specific tissue or cancer cell. A radionuclide, chemically bonded to these monoclonal antibodies, can deliver a large dose of radiation to a specific area without affecting the surrounding tissue.

Disease Management

Reduction and Elimination of Pain

Nuclear medicine serves another therapeutic function - namely, the reduction of pain. Many patients with bone cancer or cancer that has spread to the bones suffer intolerable pain. Radiotherapy can be administered to palliate the pain, replacing pain-killing drugs which eventually lose their effectiveness.

Physicians can administer a bone-seeking compound labelled with a high-LET radiation emitter. Using this nuclear technique, the level of pain is quickly lowered, or totally eliminated, providing almost instant relief to the patient.

Sterilization of Medical Devices

Medical instruments used in diagnosing or treating a patient - especially those likely to penetrate the protective skin barrier - must be totally free of germs. Inadvertent use of an unsterile medical device, such as a hypodermic syringe and needle, could transmit infection resulting in a cross-infection or, in the worst case, a fatality; in either case, contradicting the goal of medicine.

Gamma rays from cobalt-60 are used to sterilize instruments that cannot be sterilized through other methods, and at a much lower health risk. Some 150 facilities located in 44 countries worldwide provide sterile medical devices in even the most remote areas of the world.

Dosimetry

Application of accurate doses, determined for each patient through careful evaluation and calculations, is of utmost importance for the effectiveness of the application of radiation. Therefore, dosimetry, while not a diagnostic or treatment method, also plays an important role in the application of radionuclides and radiotherapy. The IAEA--in co-operation with WHO--coordinates a global network of Secondary Standard Dosimetry Laboratories (SSDLs) located in 51 Member States to improve dosimetric accuracy, particularly in radiation therapy.

These laboratories maintain the link between the users of radiation and an international measurement system calibrating the dosimeters of radiotherapy centres. Comparisons are performed for SSDLs testing the accuracy of their "secondary standard" dosimeters to ensure world wide unification of measurements.

The accuracy and the proper use of dosimeters of radiotherapy centres are also tested through the IAEA/WHO postal dosimetry service using thermoluminescent dosimeters. Since 1969, about 2000 tests were performed involving more that 700 radiotherapy centres from 89 countries.

Future Plans and Developments

The Agency has helped to raise the level of health-care in Member States through the transfer of state-of-the-art nuclear techniques, especially in less developed countries, where available facilities are either absent or grossly inadequate. The Agency conducts training courses, offers fellowships, and provides technical assistance and co-operation to optimize the manpower and equipment already available.

Future plans are aimed at the introduction of simpler techniques and specialized instruments which many laboratories in IAEA Member States lack. These will help lower expenses and increase availability of nuclear techniques in medicine.

As nuclear techniques become easier to use and therefore applicable universally, the need for appropriate and practical technology for health care and research remains an ever-changing challenge to be met by the IAEA.