The paper describes the results of retrospective epidemiological study on low dose effects of diagnostic radiation exposure to humans. The data used in the study has been collected from archives of Chelyabinsk Regional Clinical Center of Oncology and Nuclear Medicine during the project for creating the local electronic database of Ozyorsk patients examined with computed tomography (CTDB). The study group consisted of oncological patients who have received positron-emission computed tomography (PET-CT). All patients in the study group were residents of Ozyorsk – the town in South Ural where the “Mayak” production association, also known as 1st Russian nuclear enterprise is located. The main purpose of the study was to understand whether the number of PET-CT scans, as well as other radiation risk factors influences the mortality in the exposed group. The follow-up period started in 2010 since the first PET-CT scans has been performed, and ended in June, 2019. Radiation dose for oncological patients exposed to PET-CT has been compared with the cumulative dose from occupational exposure. Vital status and cause of death of patients who died to the end of follow-up has been established using the data of National Cancer Registry in part located in the Chelyabinsk Regional Clinical Center of Oncology and Nuclear Medicine. Cancer mortality has been analysed depending on age of patient, sex, number of PET-CT examinations, and presence of occupational exposure, using the logistic regression model. Main radiation risk factors influencing cancer mortality has been established.
INTRODUCTION: Peptide receptor therapy based on the 225Ac radionuclide, due to the targeted effect on tumor cells, is the most promising method of treatment for patients with generalized forms of neuroendocrine tumors and castration-resistant prostate cancer.OBJECTIVE: The aim of the work was to evaluate the effectiveness of radioligand therapy of medicinal radiopharmaceuticals with 225Ac.MATERIALS AND METHODS: Radioligand therapy based on 225Ac radionuclide was performed in 7 patients with generalized prostate cancer and 3 patients with neuroendocrine tumors.RESULTS: Systemic radiation therapy with 225Ac-PSMA 617 and 225Ac-DOTATE showed its effectiveness in clinical practice — patients have a decrease in the level of accumulation of the radiopharmaceutical (RP) in pathological foci on PET-CT with 68Ga-PSMA and 68Ga-DOTATE; a decrease in the level of prostate-specific antigen (PSA) in the blood (for prostate cancer); reduction of manifestations of asthenic, pain and carcinoid (for neuroendocrine tumors) syndromes. Dosimetric studies make it possible to assess the biodistribution of a radiopharmaceutical drug in the body, accumulation in target organs and lesions.CONCLUSION: The appointment of this type of treatment requires an integrated approach based on a thorough study of medical records, assessment of the receptor status of the tumor tissue, timely detection and prediction of adverse reactions.
Current patient release criteria established in NRB-99/2009 relate to four radionuclides used in Russia that period of the document preparation. These criteria were calculated only considering the radionuclide decay. Thus, these criteria give conservative assessments which require the patient to stay in dedicated protected room (“hot” room) of the radiotherapy department for several days and do not allow to radionuclide therapy to be given in the outpatient hospital which certainly reduces the availability of this type of treatment. Consideration of the biological excretion of the radiopharmaceutical will be able to make the patient release criteria after radionuclide therapy significantly softer. Recently, new promising radionuclides and radiopharmaceuticals for therapy have appeared, the introduction of which into medical practice is obstructed by the lack of the patient release criteria. Current study is devoted to justification of improvement the approach to definition of patient release criteria after radionuclide therapy with promising and applied radiopharmaceuticals considering biological excretion of radiopharmaceutical. As examples, calculations of patient release criteria were performed for 177Lu-PSMA, 177Lu-DOTA-TATE, 131I-mIBG и Na131I. The dosimetric model used for calculation is based on the model which was used for definition of the current patient release criteria in NRB-99/2009. Additionally, the biological excretion of the radionuclide in radiopharmaceutical, which was assessed according to the published data, was considered. Two phases of biological excretion were evaluated for considered radiopharmaceuticals (fast and slow fractions). The main contribution of the radionuclide decrease in the patient’s body during the first hours after the injection is made by the fast-eliminated fraction. During 4-6 hours after the administration about 50% of these radiopharmaceuticals eliminated via urine. The calculation of patient release criteria were performed for slow-elimination fractions which characterize the decrease of radionuclide activity in the body after the patient release. The following effective half-lives were used: 177Lu-PSMA – 60 hours, 177Lu-DOTA-TATE – 100 hours, 131I-mIBG – 45 hours, Na131I – 7.5 days. The calculations demonstrate when planning a course of radionuclide therapy with four administrations of 177Lu-PSMA, the release of a patient is allowed at the dose rate of 20 μSv/h from the patient at the distance of 1 m; in case of radionuclide therapy with 177Lu-DOTA-TATE, release of a patient is allowed at the dose rate of 12 μSv/h. Considering the fast-eliminated fraction in the first hours after the administration, it can be assumed that more patients with normal renal function can undergo radionuclide therapy with 177Lu-PSMA in the outpatient hospital. Some patients after the 177Lu-PSMA administration and patients in the therapy with 177Lu-DOTA-TATE may be held in the department in the “hot” rooms for 1-2 days until the dose rate decrease to the acceptable levels. The consideration of biological excretion of radiopharmaceutical makes it possible to soften patient release criterion for 131I-mIBG by four times and for Na131I – by 10%. It will allow to release patients after radionuclide therapy earlier without reduce of radiation safety of people around the patient and will increase the capacity of radionuclide therapy department.
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