FIELD: medicine.SUBSTANCE: group of inventions refers to medicine, namely to endocrinology, radiology, therapy, and can be used to determine individual activity of 131-iodine for radioiodine therapy of thyrotoxicosis, as well as predicting time to achieve a safe level of activity of 131-iodine in the patient's body after administering individual activity of 131-iodine. Method for determining individual activity of 131-iodine for radioiodine therapy of thyrotoxicosis involves determining the volume of (k) sections of thyroid tissue (Vk, [ml]), specific index of thyroid capture of 99mTc-pertechnetate (I, [%]), distribution of thyroid capture of 99mTc-pertechnetate over sections of thyroid tissue (Rk, [%]), as well as determination of maximum and integral thyroid capture of 131-iodine. Working solution is introduced orally in volume of 5 to 10 ml with activity content (A0) of 131-iodine from 5 to 10 MBq. Further, two dosimeters are placed on the patient's body and made with possibility of periodic recording of gamma-radiation power up to 2 mSv/h and autonomous operation up to 5 days: the first – at the level of the thyroid gland, the second – at the level of bladder. Gamma-power ofis continuously recorded for 2–5 days, where j is the number of the dosimeter, p is the number of the registered value after a certain time interval from range of 2–15 minutes, with preservation of the registered data in the dosimeter memory. Thereafter, these values are converted into activity values of 131-iodine to obtain data sets Aand Awith subsequent averaging of data for each hour of measurements to obtain arrayswhere i is number of hour after working solution introduction. Further, the therapeutic activity of the thyroid tissueis determined: if the specific index of the thyroide capture of 99mTc-pertechnetate is less than 0.5 %/ml by formulathe specific index of the thyroid capture of 99mTc-pertechnetate is more than 0.5 %/ml by formulawhereis a dose accumulation factor, and if k=1, the individual therapeutic activity of 131-iodine is taken to be a minimum value ofand if k>1, individual therapeutic activity of 131-iodine is determined by formula A=where MU is maximum thyroide capture of 131-iodine, and UI is integral capture of 131-iodine, which are determined by formulas:or by formulas:whereis an array of activity in the "Thyroid" chamber, obtained by processing the recorded data of thearrays using a four-chamber pharmacokinetics model of 131-iodine in the patient's body, taking into account the activity at each time t in the following chambers: "Body", "Thyroid", "Activity 131-iodine, derived from the body through the bladder", "The loss of 131-iodine activity as a result of radioactive decay". Time for achieving 131-iodine (T) safe level of activity in the patient is predicted after the individual activity of 131-iodine is introduced by formula:where Ais normative safety of activity for population, λ. is an effective output constant, determined by approximating an array of patient's activities in a patient's bodyby a single-exponential functionwhereis the sum of activitiesand activity in the "Body"chamber.EFFECT: method provides reducing a risk of recurrent thyrotoxicosis and more accurate prediction of the time of achieving a safe level of activity in the patient's body by determining individual activity of 131-iodine for radioiodine therapy taking into account individual pharmacokinetics.6 cl, 7 dwg, 6 ex