Assessment of the Influence of Radiation and Non-Radiation Factors on the Incidence of Gastric Cancer among Workers of the Mayak Production Association

The dissertation is devoted to an epidemiological assessment of risk factors for gastric cancer among workers of the Mayak Production Association, the first nuclear industry enterprise in Russia. The study examines the combined influence of prolonged whole-body external gamma radiation and internal alpha radiation from incorporated plutonium-239, along with non-radiation factors such as chronic gastric diseases, smoking, alcohol abuse, and prior occupational contact with chemical agents. Based on the analysis of long-term medical follow-up data, a control group is formed, relative and attributable risks are determined, and disease cases are characterized by tumor localization and degree of differentiation. The findings are intended to improve radiation protection of personnel and the organization of treatment-and-prophylactic work.

Relevance of the Study

Since the mid-twentieth century, the use of sources of ionizing radiation in industrial and medical purposes has been expanding. The development of nuclear power is of considerable economic importance. Despite the negative experience accumulated by humanity due to the lack of sufficient knowledge about the effects of radiation exposure, violations of technological processes, and the use of nuclear weapons, it is evident that scientific and technological progress and the everyday life of millions of people are inconceivable without the use of ionizing radiation; therefore, ensuring radiation safety and the protection of the population and professionals is a priority task of society.

The carcinogenic effects of ionizing radiation detected in experimental and epidemiological studies are of particular concern [100, 253]. Of considerable practical importance in medical and social terms is the assessment of the influence of radiation exposure on the occurrence of neoplasms with a high spontaneous frequency, which include gastric cancer, which occupies leading places in the structure of morbidity and mortality from malignant neoplasms worldwide [206].

The association between radiation exposure and the occurrence of gastric cancer has been demonstrated in epidemiological studies among residents of Hiroshima and Nagasaki who survived the atomic bombing, as well as among patients who underwent high-dose radiation therapy [66, 130, 181, 210]. The carcinogenic risk coefficients obtained in epidemiological studies among survivors of the atomic bombing in Japan form the basis of modern radiation safety standards. However, their transfer to other populations requires a balanced approach, especially with regard to tumors characterized by pronounced geographical differences in background morbidity and mortality, as well as in the prevalence of non-radiation risk factors [100]. The foregoing applies fully to gastric cancer. In addition, it is known that the relative biological effectiveness of different types of radiation is not uniform, and different exposure scenarios can also substantially modify the magnitude of risk [100]. Consequently, for more accurate hygienic standardization, estimates obtained both for acute and for prolonged exposure over a wide dose range are necessary.

In the majority of studies covering personnel of nuclear productions, populations residing in territories contaminated by radioactive releases and in zones of elevated natural radiation background, convincing evidence of an association between gastric cancer and prolonged radiation exposure at low doses has not been obtained [100]. Among workers of the Mayak Production Association (Mayak PA) who were subjected to prolonged exposure at high doses in the first years after the enterprise was put into operation, an increase in the frequency of malignant neoplasms, including gastric cancer, has been noted in comparison with unexposed residents of the city located near this enterprise and with national statistical indicators [31]. Gastric cancer is a polyetiological disease; therefore, for an objective assessment of its association with radiation exposure, it is necessary to take into account the influence of non-radiation factors [157].

Aim of the Study

The aim of the present study is to assess the influence of radiation and non-radiation factors on the incidence of gastric cancer among workers of Mayak PA who were subjected to prolonged whole-body external gamma radiation and internal alpha radiation from incorporated plutonium-239.

Tasks of the Study

1. To obtain information on morphologically verified cases of gastric cancer among workers of Mayak PA.

2. To form a control group among workers of Mayak PA who did not develop malignant neoplasms.

3. To study the prevalence of radiation and non-radiation risk factors among workers of Mayak PA who developed gastric cancer and among workers included in the control group.

4. To assess the risk of gastric cancer incidence among workers of Mayak PA subjected to prolonged whole-body external gamma radiation and internal alpha radiation from incorporated plutonium-239, taking into account the effect of non-radiation factors (chronic gastric diseases, smoking, alcohol consumption, occupational contact with chemical agents prior to the start of work at Mayak PA).

5. To determine the contribution of radiation and non-radiation factors to the incidence of gastric cancer among workers of Mayak PA.

Scientific Novelty of the Study

For the first time, the relative risk of gastric cancer incidence has been estimated for the personnel of Mayak PA, the first nuclear industry enterprise in Russia, subjected to prolonged exposure, taking into account the influence of non-radiation factors. An association has been revealed between the incidence of gastric cancer and prolonged whole-body external gamma radiation at high doses.

For the first time, the attributable risk has been determined, indicating that the main contribution to the incidence of gastric cancer among workers of Mayak PA is made by non-radiation factors (chronic gastric diseases, smoking, alcohol abuse).

Practical Significance of the Study

As a result of analyzing long-term medical follow-up data for the personnel of the nuclear enterprise Mayak PA subjected to prolonged whole-body external gamma radiation and internal alpha radiation from incorporated plutonium-239, an association has been established between the incidence of gastric cancer and external exposure at high doses. It has been shown that the predominant contribution to the incidence of gastric cancer among workers of Mayak PA is made by non-radiation factors (chronic gastric diseases, smoking, alcohol abuse).

The results of the study may be used to determine priorities in organizing treatment-and-prophylactic work among personnel of radiation-hazardous productions, in conducting expert evaluation to establish a causal link between gastric cancer and occupational exposure, as well as in the process of explanatory work aimed at forming an objective public opinion about the effects of ionizing radiation based on scientific facts.

Statements for Defense

1. Prolonged whole-body external gamma radiation at high doses increases the risk of gastric cancer incidence among workers of Mayak PA.

2. Internal alpha radiation from incorporated plutonium-239 has no influence on the incidence of gastric cancer among workers of Mayak PA.

3. The main contribution to the incidence of gastric cancer among workers of Mayak PA is made by non-radiation factors: chronic gastric diseases (chronic gastritis with secretory insufficiency, peptic ulcer disease), smoking, and alcohol abuse.