in medicine, a preparation that is used in the radioisotope diagnosis of disease and the radiotherapy of tumors. Radioactive preparations are either radioactive isotopes or compounds of radioactive isotopes and various inorganic or organic substances.
Of the several hundred natural and artificial radioactive isotopes, only those are used diagnostically that upon introduction into the organism either participate in the metabolic process or the organic or systematic activity under study. These radioactive preparations have a short effective half-life, which results in an insignificant radiation load on the organism being studied; the preparations are characterized by the type and energy of radiation (beta or gamma rays), which are recorded using radiometric methods.
The most widely used radioactive preparations include various compounds of 99mTc (in the diagnosis of brain tumors and in the study of central and peripheral hemodynamics), 131I and its compounds (in studies of iodine exchange and kidney and liver function), 111In and 113In (in liver studies), such colloid solutions and macroaggregates as 99mTc, 198Au, 131I, and 111In (in the study of the lungs, liver, and brain), and such gaseous radioactive preparations as 133Xe, 85Kr, and 15O (in the study of lung function and central and peripheral hemodynamics).
The major criterion used in selecting a radioactive preparation for the radiotherapy of a malignant tumor is the ability to apply a therapeutic dose of ionizing radiation to the focus of the affection, while at the same time maximally sparing surrounding tissues. This is achieved by using radioactive preparations in various aggregate states—true and colloid solutions, suspensions, granules, rods, needles, beads, wire, and bandages—and by using isotopes with optimal radiophysical characteristics (type and energy of radiation).
In clinical practice, solutions of Na131I are used in the treatment of iodine-absorbing metastases of malignant tumors of the thyroid gland; colloids and suspensions of 90Y, 198Au, and 32P are used in the interstitial and intracavitary radiotherapy of tumors; and granules, rods, beads, and needles that contain 90Y, 60Co, and 192Ir are used in the treatment of tumors of the female reproductive organs, cancer of the oral mucosa and the lungs, and brain tumors.
V. Z. AGRANAT and F. M. LIASS