Case-control study on radon exposure and lung cancer in an Italian region. Preliminary results

The present estimates of the lung cancer risk for the general population due to radon exposure in dwellings are generally obtained by extrapolating the risk estimates derived from epidemiologic studies on miner cohorts. However, due to uncertainties related to this extrapolation, numerous case-control studies in Europe and North America were planned to estimate directly the risk in dwellings. Most of these studies are still underway and, thanks to their similar design and compatible protocols, it will be possible to perform a pooled analysis in order to improve statistical power. One of these projects is being conducted in the Lazio region of Italy, which is one of the Italian regions with the highest levels of radon indoors. A total of 408 cases and 424 controls older than 34 years, who lived for 25 years or longer in the Lazio Region, were recruited in a hospital of Rome. Detailed information regarding smoking, and occupational exposure of the subjects were collected by interviews in hospital. Residential histories (periods and addresses) during the 35 years preceding the enrolment were ascertained for all study members from the local Register and from a short questionnaire to the subjects or to the next-of-kin, resulting in 2068 dwellings to be monitored within the Lazio region. The distribution of the number of dwellings among cases and controls was the following: 25.7% of the cases and 27.3% of the controls had lived all the preceding 35 years in a single dwelling, whereas only a minority (7.9%) changed five addresses or more. The mean number of dwellings was very similar among cases (2.47) and controls (2.50). In each dwelling, radon dosemeters were placed in both the main bedroom and living room for two consecutive six-month periods. In the second six-month period, two thermoluminescent dosemeters were also collocated in each monitored room to measure gamma radiation emitted by the building materials, in order to evaluate more comprehensively the exposure of population to natural radioactivity. The radon dosemeters were first placed between September 1997 and June 1998. In 1327 dwellings the dosemeters were positioned in the index dwelling, whereas in 474 a similar dwelling was measured (i.e., a dwelling in the same building, and at approximately the same floor). All together, more than 85% of the target 2068 dwellings were monitored. Radon and gamma dosemeter collection was concluded in August 1999, and data analysis is ongoing. The preliminary results on about 4800 radon dosemeters exposed for six-month periods (about 3500 dosemeters for the first six-month period in about 1750 dwellings, and about 1300 for the second six-month period in about 650 dwellings) are the followings: average =100 Bq/m3, geometric mean =75 Bq/m3, geometric standard deviation =2.1, 10%>200 Bq/m3, 2.2%>400 Bq/m3. These data confirm that the presence of indoor radon in Lazio region is significant. More detailed and complete results are expected to be available by January 2000. (author)