Cancer incidence among Bulgarian medical radiation workers: epidemiological study

To look for the cancer incidence in a cohort of medical radiation workers in relation to work history (year of first employment, duration of occupational exposure, and radiation doses received for the whole period).

In this retrospective study the cancer incidence among 315 medical workers (radiotherapists, diagnostic radiologists and technical personnel) was compared with that of 320 other medical specialists not having occupational contacts with radiation sources, who worked in hospitals in the territory in Sofia for the period 1960-2000. Data concerning incident cancer occurrence were obtained via a questionnaire. Data for individual doses were extracted from the National System of Individual Dosimetric Control. Descriptive statistics, x(2) test, Fisher's exact test and ANOVA analysis were used.

Cancer was more frequently diagnosed among radiation workers compared to other medical specialists (p=0.018). When analyzing by cancer type breast cancer was more frequently diagnosed in radiation workers (p=0.037). No significant relation was observed between cumulative radiation dose and cancer incidence (p=0.12), or cancer incidence by different cancer localizations (p=0.13). Similarly, no difference was found between year of first employment and cancer development in cases and controls (p=0.854 and p=0.178, respectively). Longer whole working period was significantly connected with lower cancer incidence in cases (p=0.015 and p=0.062 for cases and controls, respectively).

The present study shows that cumulative dose and the duration of work in an ionizing radiation environment does not substantially influence cancer development. Although we found higher cancer occurrence among cases compared to controls, those two factors do not give us ground to confirm that working in an ionizing radiation environment increases cancer incidence. It is important to continue the monitoring of the health status of medical radiation workers.