First analysis of cancer incidence and occupational radiation exposure based on the National Dose Registry of Canada.

A cohort study was conducted to investigate the relation between cancer incidence and occupational exposure to ionizing radiation. Records containing dose information from 1951 to 1988 for 191,333 persons were extracted from the National Dose Registry of Canada. The records were linked to the Canadian Cancer Data Base, with incidence data from 1969 to 1988. Standardized incidence ratios were calculated using Canadian cancer incidence rates stratified by age, sex, and calendar year. Excess relative risks were obtained from internally based dose-response analyses. The following significant results were found for males and females combined: a deficit in the standardized incidence ratio for all cancers combined; elevated standardized incidence ratios for thyroid cancer and melanoma; and elevated excess relative risks for rectum, leukemia, lung, all cancers combined, all except lung, and all except leukemia. For males, cancers of the colon, pancreas, and testis also showed significantly elevated excess relative risks. The specific cancer types listed above have been implicated in previous studies on occupational exposure to ionizing radiation, except for testis, colon, and melanoma, while the findings on thyroid cancer from previous studies are inconclusive. The thyroid standardized incidence ratios in this study are highly significant, but further investigation is needed to assess the possibility of association with occupational radiation exposure.

A summary of data on accumulated occupational radiation doses among Canadian workers.

This paper is based on work done on accumulated career doses. The data are taken from the National Dose Registry and consist of accumulated doses to the monitored workforce from the years 1970, 1975, 1980, 1985, and 1990. Four broad occupational categories are analyzed: medicine, nuclear power, uranium processing (including mining, milling, refining, and fuel fabrication), and industry. Two- and three-dimensional bar charts are used to display workforce sizes, collective accumulated doses, and average accumulated doses over time, broken down by career start. Lognormal plots are used to show the distribution of accumulated doses. Many trends are as could be expected, and some of those may be used for construction of statistical models for career-dose accumulation. The size and accumulated career doses in the workforces of the uranium processing category do not vary regularly with time, and in this case modeling is likely to be difficult.

Doses and population irradiation factors for Canadian radiation technologists (1978 to 1988).

Individual and collective radiation doses received by Canadian radiation technologists (RTs) working in diagnostic radiology, nuclear medicine and radiotherapy are summarized for the period 1978 to 1988. The data were obtained directly from the National Dose Registry, Department of National Health and Welfare. Over the 11-year study period the mean annual dose equivalent fluctuated around 0.2, 1.8 and 1.1 mSv for RTs working in diagnostic radiology, nuclear medicine and radiotherapy respectively. Over the same period the occupational collective dose equivalent decreased in diagnostic radiology (by 44%) and radiotherapy (by 35%) and increased in nuclear medicine (by 45%). Approximately 10,000 RTs are monitored each year, with an estimated total occupational collective dose equivalent of about 3.6 person-sieverts. Analysis of dose distribution data showed that only 1.3% of all monitored RTs received an annual whole-body dose equivalent greater than the current legal limit for members of the public (5 mSv). Approximately half of the RTs working in nuclear medicine and radiotherapy received an annual dose equivalent in excess of 0.5 mSv; only 7.3% of their diagnostic radiology counterparts exceeded this level. Demographic data showed a high preponderance of young women in all three RT classifications, and an analysis of the radiation risks to this occupational group revealed increases of up to 12% above the risk associated with a "standard" adult working population exposed to the same collective dose equivalent.

Occupational doses to medical radiation technologists in Manitoba (1978-1988).

In Canada, occupational exposure to medical technologists accounts for about 8 per cent of all occupational exposure. In this paper, occupational doses to Manitoban radiation technologists (RTs) in diagnostic radiology, nuclear medicine and radiotherapy are presented for the period 1978-1988. Particular attention is paid to the distribution of dose among this population. The importance of age and sex demographics on radiation detriment is also estimated.

Projected whole-body career doses for radiation workers in Canada.

Projected whole-body career doses have been calculated from Canadian exposure data contained in the National Dose Registry, using the straight extrapolation of accumulated annual doses to a 40-y period, as described in the 1977 UNSCEAR report (UNSCEAR77). The calculations are broken down by type of employment. The results are compatible with earlier publications. Double regressions provided trends of projected career doses with increasing length of employment and with progressing date of enrollment into the registry. The career doses fit a log-normal or a hybrid log-normal distribution for occupations with low and high exposures, respectively.