Radioisotopes are also widely used in scientific research, and are employed in a range of applications, from tracing the flow of contaminants in biological systems, to determining metabolic processes in small Australian animals.
Radioisotopes are used in many areas of research and science. The age of water from underground bores can be estimated from the activity of naturally occurring radioisotopes in the water, informing decisions regarding the use of groundwater for consumption.
Openair nuclear weapons testing in the 1950s and early 1960s nearly doubled the amount of carbon-14 in the atmosphere. Scientists can use the increased number of carbon-14 atoms in the environment as tracers to measure soil movement and land degradation. For example, by the amount of carbon-14 in organic material within sediments, scientists can determine if it was deposited in sedimentary layers before or since this period of weapons testing. Levels of certain radioisotopes in environmental samples can be measured to check whether nations are in compliance with agreements concerning the development of nuclear weaponry.
Nuclear activities may produce routine or accidental releases of radioactive material into the environment. Iodine-129 and uranium-236 can be measured in environmental samples, and are signatures of nuclear activities such as reprocessing irradiated nuclear fuel. Nuclear medicine uses small amounts of radiation to provide information about a person’s body and the functioning of specific organs, ongoing biological processes, or the disease state of a specific illness. In most cases, the information is used by physicians to make an accurate diagnosis of the patient’s illness. In certain cases radiation can be used to treat diseased organs or tumours.
Radiotracer techniques are often used to validate mathematical models of sediment and contaminant transport in the coastal zone and so contribute to sustainable development. Even minute amounts of radioactive material can be detected easily, which makes it ideal for use in tracing the movements of water, gases or even insects. Radioactive tracers mixed with sewage are used to track sewage dispersion.
A similar technique is used to trace small leaks in complex systems such as power station heat exchangers. Flow rates of liquids and gases in pipelines can be measured accurately, as can the flow rates of large rivers, all with the assistance of radioisotopes
Nuclear medicine uses small amounts of radiation to provide information about a person’s body and the functioning of specific organs, ongoing biological processes, or the disease state of a specific illness. In most cases, the information is used by physicians to make an accurate diagnosis of the patient’s illness. In certain cases radiation can be used to treat diseased organs or tumours.
Scientists have identified a number of chemicals that are absorbed by specific body tissues and organs. They are called targeting agents or molecules. The brain, for example, consumes large quantities of glucose. Using similar knowledge, radiopharmacists can choose the appropriate targeting chemical, label it with an appropriate radioisotope and use it as a radioactive tracer for a particular body tissue, organ or function.
Once the substance has been tagged with a radioisotope and introduced into the body, it is incorporated into the normal biological processes and excreted in the usual ways. Diagnostic radiopharmaceuticals can be used to examine blood flow to the brain; to assess functioning of the liver, lungs, heart or kidneys; to assess bone damage; and to confirm other diagnostic procedures. They are used in sports medicine to diagnose stress fractures, which are not generally visible in X-rays.
Radiopharmaceuticals are used in very small quantities for diagnostic work – just enough is administered to obtain the required information before the radiopharmaceutical decays or is excreted from the body. The radiation dose received is similar to that from diagnostic X-rays. The non-invasive nature of this technology, together with its ability to reveal organ function, makes it a powerful diagnostic tool. The most common radioisotopes used for diagnosis are technetium-99m, distantly followed by iodine-123, fluorine-18, thallium-201 and gallium-67
Rapidly dividing cells are particularly sensitive to damage by radiation. For this reason, some cancerous growths can be controlled or eliminated by irradiating the area. This is called radiotherapy. With internal radiotherapy, the radioisotope that generates the radiation is localised in the affected organ. This is achieved by administering it as a radioactive element that is taken up by that part of the body, or by attaching the radioactive element to a biological compound, which lodges in the body at the disease site. Iodine-131 is used for internal radiotherapy, to treat thyroid cancer and hyperthyroidism (an over-active thyroid).
Another radiopharmaceutical, incorporating samarium-153 and known commercially as Quadramet, is used internally to reduce the pain from secondary bone cancers associated with breast, prostate and some other cancers. Quadramet is preferable to traditional pain killers such as morphine because it improves the patient’s quality of life, allowing them to be more lucid during time spent with family. Considerable research is being conducted worldwide into the use of radioisotopes attached to highly specific biological compounds. The eventual tagging of these compounds with a therapeutic dose of radiation may lead to the regression or even cure of some diseases, and many scientists are enthusiastic about the potential of these radioisotopes.
External radiotherapy is carried out using a radioactive source that is outside the body. The radiation beam is directed towards the diseased tissue so the beam can deliver a high dose of radiation while sparing the surrounding healthy tissue. Brachytherapy uses a source implanted in the body at the site to be irradiated. Brachytherapy sources can be placed on the skin or implanted internally, and can be temporary or permanently left in the patient. Where the source is internal, various radioisotopes can be used.
Iridium-192, for example, is produced in wire form and introduced through a catheter to the target area – usually in the head or breast. The implant is left in for the required time and then removed to shielded storage. The procedure is cheaper than using external radiation and gives less overall radiation to the body. Prostate cancer brachytherapy is an increasingly popular form of treatment of prostate cancer. Low dose rate seeds of iodine-125 are implanted into the prostate and permanently left in the patient.