Dynamics Of Peripheral Blood Parameters in Different Periods of Chronic Radiation Syndrome after Chronic Exposure with Different Dose Rates

Purpose: To study the effect of the radiation dose rate on the dynamics of peripheral blood indicators in various periods of chronic radiation syndrome (CRS), which developed as a result of professional prolonged radiation exposure in a cohort of former employees of the Mayak plant who underwent inpatient examination at the clinic of the A.I. Burnazyan Federal Medical Biophysical Center of the FMBA of Russia in the period up to 1995. Material and methods: The study of the dynamics of absolute peripheral blood indices in former employees of Mayak plant who were exposed to prolonged industrial radiation with a dose rate of less than 0.001 Gy/day (25 people), 0.003‒0.007 Gy/day (12 people) and 0.008‒0.07 G/day (15 people) during the periods of formation, outcomes and immediate, as well as long-term consequences of CRS. Statistical processing of the material was performed using the IBM SPSS Statistics software package 23.0 using the Kruskal–Wallis criteria and the Mann–Whitney U-test for independent samples. The results obtained were considered statistically reliable at p < 0.05. Results: In a group of patients irradiated with a dose rate of 0.008‒0.07 Gy/day during the periods of formation, as well as the outcomes and immediate consequences of CRS, platelet-, leuco- and deep neutropenia were noted. A decrease in the number of erythrocytes and hemoglobin was detected only in the period of outcomes and immediate consequences. The development of agranulocytosis and anemic syndrome are signs that distinguish the course of CRS in this group of patients from the clinical picture of typical CRS. In the period of long-term consequences, 60 % of patients (9 out of 15) developed oncohematological diseases. At an irradiation power of 0.003‒0.007 Gy/day anemic syndrome was found in 4 out of 12 patients. Leukopenia was observed in the periods of outcomes and immediate consequences. Granulocytopenia was detected in all three periods of the course of CRS. In the long term, 2 patients from this group developed oncohematological diseases At an irradiation power of less than 0.001 Gy/day shallow thrombocytopenia and neutropenia are noted in the periods of outcomes and immediate consequences of CRS. In the period of long-term consequences, all the average values of peripheral blood indicators correspond to normal levels. Conclusions: With prolonged irradiation of a person with a dose rate of 0.008‒0.07 Gy/ day or more, with the accumulation of a total dose of 1.7‒9.6 Gy and a contact duration of 6‒96 months, one can expect the development of CRS with a peculiar subacute clinical course of bone marrow syndrome (BMS), manifested by the defeat of all three hematopoietic sprouts, the development of agranulocytosis, anemia and, probably, in 60 % of cases of leukemia development with an unfavorable prognosis for the patient’s life. The main factor determining this feature of the course of BMC CRS is the dose rate, which exceeds 0.008 Gy / day (2 Gr/year). At a dose rate of 0.003‒0.007 Gy / day (0.7‒1.7 Gy / year), the course of CRS with the development of agranulocytosis is possible in 25 %, anemia – in 33 % of observations. This course of the disease is most likely with a dose rate approaching the upper limit of the named range and high total doses. In other cases, the course of the disease is favorable. In the long-term period, moderate, transient leuko-, neutro- and thrombocytopenia are possible. With prolonged irradiation with a dose rate of less than 0.001 Gy / day (0.25 Gy / year), the course of the disease is relatively favorable with almost complete restoration of hematopoiesis in the long term.