Dr. Tarveen Karir
Radiation Medicine Centre Division, BARC
Dr. Tarveen Karir joined Radiation Medicine Centre Division of BARC in 1987 after completion of her M.Sc. in Analytical Chemistry from Nagpur University and got her early exposure of work related with in-vivo nuclear medicine, both, development of newer radiopharmaceuticals for imaging various organs and routine scintigraphy. She did her Ph.D work in the area of development of solid phase immunoassays for haptens from Mumbai University in the year 2006. Presently she is working as Manager, Scientific Information Resources & Publications Section of Board of Radiation & Isotope Technology (BRIT), Navi Mumbai.
Title: Applications of Radioisotopes in Medicine & Healthcare
The attributes of naturally decaying atoms, known as radioisotopes, gives rise to several applications across many aspects of modern day life. The applications of radioisotopes in the field of healthcare in general, and in medicine in particular, have been very extensive. There is widespread awareness of the use of radiation and radioisotopes in medicine, particularly for diagnosis (identification) and therapy (treatment) of various medical conditions.
Nuclear medicine uses radiation to provide information about the functioning of a person's specific organs, or to treat disease. In most cases, the information is used by physicians to make a quick diagnosis of the patient's illness. The thyroid, bones, heart, liver, and many other organs can be easily imaged, and disorders in their function revealed. In some cases radiation can be used to treat diseased organs, or tumours.
Radioisotopes are an essential part of medical diagnostic procedures. In combination with imaging devices which register the gamma rays emitted from within, they can study the dynamic processes taking place in various parts of the body.
Diagnostic radiopharmaceuticals: Every organ in our bodies acts differently from a chemical point of view. Doctors and chemists have identified a number of chemicals which are absorbed by specific organs. The thyroid, for example, takes up iodine, whilst the brain consumes quantities of glucose. With this knowledge, radiopharmacists are able to attach various radioisotopes to biologically active substances. Once a radioactive form of one of these substances enters the body, it is incorporated into the normal biological processes and excreted in the usual ways. These radioactive substances specific for a particular organ is known as Radiopharmaceuticals. In using radiopharmaceuticals for diagnosis, a radioactive dose is given to the patient and the activity in the organ can then be studied either as a two dimensional picture or, using tomography, as a three dimensional picture. Diagnostic techniques in nuclear medicine use radioactive tracers which emit gamma rays from within the body. These tracers are generally short-lived isotopes linked to chemical compounds which permit specific physiological processes to be scrutinised. They can be given by injection, inhalation, or orally. The amount of the radiopharmaceutical given to a patient is just sufficient to obtain the required information before its decay. The radiation dose received is medically insignificant. The patient experiences no discomfort during the test and after a short time there is no trace that the test was ever done. The non-invasive nature of this technology, together with the ability to observe an organ functioning from outside the body, makes this technique a powerful diagnostic tool. The radioisotope most widely used in medicine is Tc-99, employed in some 80% of all nuclear medicine procedures. It is an isotope of the artificially-produced element technetium and it has almost ideal characteristics for a nuclear medicine scan, such as with SPECT. For PET imaging, the main radiopharmaceutical is fluoro-deoxy glucose (FDG) incorporating F-18 – with a half-life of just under two hours – as a tracer. The FDG is readily incorporated into the cell without being broken down, and is a good indicator of cell metabolism.
Nuclear medicine therapy: The uses of radioisotopes in therapy are comparatively few, but nevertheless important. Cancerous growths are sensitive to damage by radiation. For this reason, some cancerous growths can be controlled or eliminated by irradiating the area containing the growth. Iodine-131 is commonly used to treat thyroid cancer, probably the most successful kind of cancer treatment. It is also used to treat non-malignant thyroid disorders. Many therapeutic procedures are palliative, usually to relieve pain. For instance, Strontium-89 and (increasingly) Samarium-153 are used for the relief of cancer-induced bone pain. Rhenium-186 is a newer product for this. Lutetium-177 dotatate or octreotate is used to treat tumours such as neuroendocrine ones, and is effective where other treatments fail. A series of four treatments delivers 32 GBq. After about four to six hours, the exposure rate of the patient has fallen to less than 25 μSv per hour at one metre and the patients can be discharged from hospital. Lu-177 is essentially a low-energy beta-emitter (with some gamma) and the carrier attaches to the surface of the tumour.
Radiation therapy: External irradiation (sometimes called teletherapy) can be carried out using a gamma beam from a radioactive cobalt-60 source, though in developed countries the much more versatile linear accelerators are now being used as high-energy X-ray sources (gamma and X-rays are much the same). An external radiation procedure is known as gamma knife radiosurgery, and involves focusing gamma radiation from 201 sources of Co-60 on a precise area of the brain with a cancerous tumour. Worldwide, over 30,000 patients are treated annually, generally as outpatients. Teletherapy is effective in the ablation of tumours rather than their removal; it is not finely tuned.
Internal radionuclide therapy is administered by planting a small radiation source, usually a gamma or beta emitter, in the target area. Short-range radiotherapy is known as brachytherapy, and this is becoming the main means of treatment. Iridium-192 implants are used especially in the head and breast. They are produced in wire form and are introduced through a catheter to the target area. After administering the correct dose, the implant wire is removed to shielded storage. Permanent implant seeds (40 to 100) of iodine-125 or palladium-103 are used in brachytherapy for early stage prostate cancer. Alternatively, needles with more-radioactive Ir-192 may be inserted for up to 15 minutes, two or three times. Brachytherapy procedures give less overall radiation to the body, are more localized to the target tumour, and are cost-effective.