Revision 1
March 19, 1998
by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.2.6
Natural Radiation and Radioactivity

1.2.6.2
Natural Background: Populations

"The major objective of the study is to estimate cancer risk associated with the low level radiation exposure in HBRA. Early cancer mortality data (1970-1978) were collected by a retrospective survey and the data from 1979 were obtained by a prospective survey through a death registry system established in the investigated areas. Up to the end of 1986, 467 cancer deaths were found among 1,008,769 person-years (PYr) at risk in HBRA. The corresponding figures in CA were 533 cancer deaths and 995,070 PYr. The general conclusion was that the cancer mortality in HBRA was lower than that in CA, though the difference was not statistically significant (Wei et al 1990)."

"There were 231 cancer deaths (160 in HBRA and 71 in CA) and 1990 non- cancer deaths (1,441 in HBRA and 549 in CA) among 421,640 PYr at risk in the cohort (311,237 in HBRA and 110,403 in CA) during the period of 1987 to 1990. The total death rate (per 100,000 PYr) during this period is 514.40 in HBRA, and 561.58 in CA. The first six causes of deaths are the same in each group.

"The crude mortality rate of overall cancers (per 100,000 PYr) is 51.41 in HBRA and 64.31 in CA. The order of first four site-specific cancer deaths in HBRA is cancers of liver, nasopharynx, stomach and lungs. It is almost the same in CA, only the sequence of nasopharynx cancer and stomach cancer changed each other.

"The RRs adjusted for age group and sex for each dose group in HBRA compared with CA for overall cancers and for all cancers except leukemia are less than 1 except for low dose group, and there seems to be a trend of RR decrease with the increase of exposure dose from natural radiation, though there is no statistically significant difference. As for the site- specific cancer studied, the cancers of lungs, liver, stomach, nasopharnyx and leukemia, the RRs are also less than 1 except for nasopharnyx cancer and for leukemia in high dose group (Table l). Although the sample size in each group was not large enough to make definite conclusion, the observation of current follow-up period reproduced the previous results obtained from the data up to 1986 that the cancer mortality in HBRA is generally lower than that in CA.

"....However, the results from the combined data confirmed previous results with stronger power of test that the cancer mortality in HBRA is in general lower than that in CA."