RU2289458C2 - Method for verification of dose during medical administration of open radioactive nuclides - Google Patents

Abstract

FIELD: medicine, namely, medicinal use of radiation, possible use for determining dose really received by pathologic focus having absorbed open radioactive nuclide.

SUBSTANCE: method for verification of dose during medicinal usage of open radioactive nuclides includes measuring intensiveness of radiation, with consideration of changes in radiation source activity in time, during that, by means of tissue-equivalent phantom, original intensiveness of radiation of open radionuclide is measured immediately prior to injecting it into organism of patient as well as average intensiveness of radiation from focuses having absorbed radionuclide, and after that individual relative dose of open radionuclide injected into pathologic focuses is computed using formula

where D_n/o - value of relative dose in %, I_o - original intensiveness of radiation at the moment of injection of radionuclide, I_n - average intensiveness of radiation from focuses at day or hour of measurement of n, B₀ and B_n - background values of radiation intensiveness at the moment of injection of radionuclide and at the day of measurement, respectively, k - coefficient of daily or hourly decomposition of radionuclide, n - number of days or hours having passed since the moment of injection of radionuclide.

EFFECT: invention allows verification of relative dose in most precise and individual manner.

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Description

The invention relates to medicine, namely to nuclear medical use, and is intended to determine the dose that is actually received by the pathological focus that has absorbed the open radionuclide, introduced into the patient's body in the form of a radiopharmaceutical for diagnostic or therapeutic purpose.

Measurement of the absolute value of the dose is known in the medical use of radiation. To measure the dose from a radionuclide absorbed by a focus (or multiple foci) with gamma radiation, it is necessary to use sensitive recording equipment, as well as determine the masses of target organs and calculate the corresponding absorbed fractions [1, 2].

At the same time, the measurement of the absorbed dose of beta-emitting radionuclides introduced into the body, whose beta radiation has a short range in biological tissues and is therefore not accessible for direct external recording, remains a big problem. Recently, the literature [2] presents the possibility of external radiometry of beta emitters included in pathological foci, according to inhibitory gamma radiation, which is generated by beta particles when they are slowed down in tissues.

However, these known methods of dosimetry of ionizing radiation in the medical use of open radionuclides embedded in pathological foci have a number of significant drawbacks. These methods include calculating the dose of internal radiation with a total consideration of both the geometric and mass parameters of pathological lesions obtained by dynamically repeating the use of medical imaging tools (for example, x-ray studies or scintigraphy), and a number of mathematical expressions related to the nuclear physical characteristics of the used radionuclide. These methods differ on the negative side, firstly, the long multi-day implementation of the calculation procedure itself, and secondly, a prerequisite for a multi-stage determination of the dose characteristics of internal radiation. Moreover, each of the stages is accompanied by a certain measurement or calculation error, which generally creates a very large total error in determining the absorbed dose.

In addition, the measurement of absolute focal, organ, and total radiation doses, which is further aggravated by low accuracy, largely serves the tasks of dose accounting and control within the framework of ensuring radiation safety and does not take into account the peculiarities of the metabolic processes of incorporating an open radionuclide into pathological foci that are strictly individual for each specific patient. However, the latter have the greatest clinical significance.

The aim of the invention is the verification of the most accurate and individual relative dose introduced into the pathological foci of an open radionuclide.

This goal is achieved by determining not the absolute absorbed dose in the foci, but the relative dose, which depends, on the one hand, on the activity of the open radionuclide initially introduced into the body, and on the other hand, on its accumulation in the pathological foci, which, in turn, , due to metabolic processes in the body of a particular individual. In this case, the initial radiation intensity is measured through a tissue-equivalent phantom immediately before the introduction of the radionuclide into the patient’s body and the average radiation intensity from the foci that absorbed the radionuclide, taking into account the change in the activity of the radiation source over time, and the relative dose is calculated by the formula

where D _{n / o} - the value of the relative dose in%,

And _o is the initial radiation intensity at the time of the introduction of the radionuclide,

And _n is the average radiation intensity from the foci per day (or hour) of measurement n,

Ф _о and Ф _n are the background values of the radiation intensity at the time of introduction of the radionuclide and on the day of measurement, respectively,

k is the coefficient of daily (hourly) decay of the radionuclide,

n is the number of days (hours) elapsed since the introduction of the radionuclide.

It is taken into account that the change in the radiation intensity is directly proportional to the daily (hourly) activity of the radionuclide.

The specified combination and sequence of distinctive actions are not known and do not follow explicitly from the existing level of science and technology, therefore, the claimed method corresponds to the inventive step.

The method is as follows. The radiation intensity is measured in the room in which the measurement is carried out (Ф _о ). Then, through the tissue-equivalent phantom, the radiation intensity of an open radionuclide is measured, which is to be introduced into the patient's body in the form of a radiopharmaceutical with a diagnostic or therapeutic purpose (I _o ). After the injection of the radiopharmaceutical on the day or hour (n) necessary for the measurement, which has elapsed since the injection, the radiation intensity in the room (Ф _n ) is recorded with the same measuring device, then the intensity of the patient is measured over the foci that have accumulated the radionuclide, and its average value is calculated ( And _n ). After that, calculate the value of the relative dose of the radionuclide actually accumulated in the pathological foci of the patient, in relation to the initially introduced into his body according to the formula

where D _{n / o} - the value of the relative dose in%,

And _o is the initial radiation intensity at the time of the introduction of the radionuclide,

And _n is the average radiation intensity from the foci per day (or hour) of measurement n,

Ф _о and Ф _n are the background values of the radiation intensity at the time of introduction of the radionuclide and on the day of measurement, respectively,

k is the coefficient of daily (hourly) decay of the radionuclide,

n is the number of days (hours) elapsed since the introduction of the radionuclide.

The dose verification of the proposed method was carried out by us in 7 patients who were injected with an open radionuclide in the form of a solution of strontium chloride for therapeutic purposes. The determination of the relative dose made it possible for all these patients to individually assess the duration and degree of accumulation of the radionuclide in the pathological foci, the relative value of the real radiation dose and the associated clinical effect, which influenced the tactics of further treatment.

We present clinical examples of the use of the method.

Example 1. Patient D., 57 years old, clinical diagnosis: Prostate cancer, generalization of the process with metastatic damage to Th6, Th12, L1 vertebrae, sternum, 3-5 ribs on the left, right iliac bone, severe pain. For the purpose of systemic radiation therapy, the patient received an intravenous injection of 148 MBq of radionuclide strontium-89 chloride. Immediately before the injection, the radiation intensity of the radiopharmaceutical through the tissue-equivalent phantom was recorded, which amounted to 1175 imp / sec / cm ² ; the average radiation intensity from the foci is determined on the 5th, 7th, 12th days from the moment of the introduction of the radionuclide and according to the claimed method, the relative dose was calculated, which amounted to 38.14; 26.13; 16.7%, respectively. As a result, the systemic effect of the radionuclide was rated as relatively satisfactory, which required additional pharmacotherapy. At the control examination after 3 months the patient's condition is satisfactory, there is no pain syndrome.

Example 2. Patient A., 47 years old, clinical diagnosis: Cancer of the left breast with multiple metastases in the pelvic bone, right scapula, left humerus, 6-7 ribs on the left, pain. The radiation intensity of strontium-89 radionuclide was measured immediately before the administration of the radiopharmaceutical and over the bone foci in the patient on the 2nd, 6th, 10th, and 14th days from the moment of injection. The relative dose values on these days were 80.25, respectively; 90.16; 53.38; 20.28%, which allowed us to evaluate the systemic radiation effect of the radiopharmaceutical as satisfactory. The pain syndrome is completely stopped after 7 days. At the control examination, the patient's condition is satisfactory, pain is absent.

Example 3. Patient K., 56 years old, clinical diagnosis: Peripheral cancer of the upper lobe of the left lung, condition after surgical treatment, multiple metastases in the Th5-Th8 vertebrae, severe pain. Systemic radiation therapy was carried out by intravenous injection of 148 MBq of strontium-89 chloride. The radiation intensity of strontium-89 immediately before injection was 1180 imp / sec / cm ² . The relative dose of the claimed method is determined on the 2nd, 5th, 9th days after the administration of the radiopharmaceutical and amounted to 18.36; 20.3; 16.48% respectively. The effect of the radiopharmaceutical was assessed as unsatisfactory, the pain syndrome of the same degree persisted until the 9th day, even with the additional use of medicinal analgesics, which required irradiation of the most painful Th5-Th7 vertebrae by means of remote gamma therapy; pain syndrome partially stopped.

Thus, the inventive method allows for verification of the most accurate and individual relative dose of an open radionuclide introduced into pathological foci.

Literature

1. Gorlachev G.E. Measurement of absolute doses in radiation therapy // Honey. physics. - 2000. - No. 7. - S.83-92.

2. Narkevich B.Ya., Kostylev V.A., Shiryaev S.V. Dosimetric support of radionuclide therapy // III congress of MOO "Society of nuclear medicine", All-Russian scientific-practical conference "Actual issues of nuclear medicine and radiopharmaceuticals". School "Selected Issues in Nuclear Medicine": Abstracts. - Dubna, 2004 .-- P.64-71.

Claims (1)

The method of dose verification in the medical use of open radionuclides by measuring the radiation intensity taking into account the change in the activity of the radiation source over time, characterized in that the initial radiation intensity of the open radionuclide is measured directly before its introduction into the patient’s body and the average radiation intensity from the foci that absorbed the radionuclide through a tissue equivalent phantom after which the individual relative dose of the open radionuclide introduced into the pathological foci is calculated and according to the formula

where D _{n / 0} is the value of the relative dose,%; And ₀ is the initial radiation intensity at the time of the introduction of the radionuclide; And _n is the average radiation intensity from the foci per day or hour of measurement of n; Ф ₀ and Ф _n are the background values of the radiation intensity at the time of introduction radionuclide and on the day of measurement, respectively; k is the coefficient of daily or hourly decay of the radionuclide; n is the number of days or hours that have passed since the introduction of the radionuclide.