Incidence of Cancer Due to Exposure to Ionizing Radiation: A Cohort of Nuclear Sector Workers in the City of São Paulo.

Abstract

Objective: To compare cancer incidence between workers exposed to ionizing radiation in an organization based in São Paulo and the general population of the city, as well as between monitored and unmonitored subgroups for gamma- and X-irradiation within this worker population.

Methods: A retrospective open cohort study based on data from workers employed from 08/31/1956 to 12/31/2016, collected from the organization and official institutions. Standardized incidence ratios (SIRs) were calculated, stratified by sex, age, and calendar period, for cancer groupings by type, risk factor, organ system, and morphological aspect. Two analyses were performed: the external analysis, which compared the cancer incidence of the study population with that of the general population of São Paulo, and the internal analysis, which compared the cancer incidence of the monitored subgroup with the unmonitored subgroup for gamma and X-irradiation.

Results: The external incidence analysis showed an SIR = 0.590 (95% CI 0.537; 0.647, p < 0.001), and the internal incidence analysis showed an SIR = 1.066 (95% CI 0.950; 1.192, p = 0.277).

Conclusion: This study showed that cancer incidence was lower among all workers compared to the general population, and there was no increase in cancer incidence among those monitored for gamma and X-irradiation compared to the unmonitored subgroup. An increased incidence of thyroid cancer was observed among monitored workers and among male monitored workers.