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

1.2.6.3
Radon

1.2.6.3.1
Ecological Studies

"Misasa town in Tottori prefecture, where radon spa has been operating for long time, consists of high radon background area with relatively large and stable population."

"Misasa town was divided into high and low exposure areas, with mean indoor radon levels about 60 and 20 Bq/m3, respectively. A cohort of 4,331 residents (3,083 and 1,248 subjects in high and low exposure areas, respectively) whose ages were 40 or older on Jan 1, 1976, were followed until Dec 31, 1993....Standardized Incidence Ratio (SIR) was calculated using the incidence of Tottori prefecture as a standard rate."

"Compared to the incidence of Tottori prefecture, the incidences from cancer in Misasa town were generally low, though not statistically significant except that for female in high exposure area (SIR=0.76, 95% Confidence Interval=0.62-0.91). Especially the incidences from stomach cancer in high exposure area were significantly lower for male (SIR=0.72, 95% CI=0.53-0.96).

"When compared directly between high and low exposure area, rate ratios in high exposure area for all site cancers, stomach cancer and lung cancer were 1.06 (95% CI, 0.79-1.42), 0.70 (95% CI, 0.44-1.11) and 1.65 (95% CI, 0.83-3.30) for male, and 0.90 (95% CI, 0.65-1.24), 0.58 (95% CI, 0.34- 1.00), 1.07 (95% CI, 0.28-4.14) for female, respectively.

"No difference was observed on incidence from all-site cancers between high and low exposure area, while stomach cancer incidence seemed to decrease and lung cancer incidence seemed to increase in high exposure area. Caution is needed for interpretation, however, since individual exposure level was not measured and major confounding factors, such as smoking, could not be controlled in this study."