57
EXPERIENCE FROM RETROSPECTIVE RADON EXPOSURE ESTIMATIONS FOR INDIVIDUALS IN A RADON-EPIDEMIOLOGICAL STUDY USING SOLID STATE
NUCLEAR TRACK DETECTORS.

R. Falk 1 , K. Almrén 2 and I. Östergren 1
1 Swedish Radiation Protection Institute (SSI), SE-171 16 Stockholm, Sweden 2 Division of Environmental Epidemiology, National Institute of Environmental Medicine
Karolinska Institutet, SE-171 77 Stockholm, Sweden.

The relation between an increased risk for lung cancer and exposure to indoor radon is assessed in
epidemiological studies. Both the quality and reliability of smoking data and the radon exposure
data are of primary importance. Contemporary measurement of radon concentration in the
dwellings of the individuals in a case-control study is traditionally used to assess the past radon
history. These assessments contain large uncertainties since the contemporary measured radon
concentration might not be representative for the situation a long time ago. The measurement of
the long-lived decay products from 222 Rn remaining on indoor hard surfaces, such as glass,
presents another possible way to assess the exposure to indoor radon.
At the Swedish Radiation Protection Institute, a combination of two different solid state nuclear
track detectors has been developed to assess the 210 Pb activity implanted in glass surfaces by
measurement of 210 Po alpha activity. This detector (a RETRO detector) is used in the Swedish
radon epidemiological case-control study of non-smokers where the objectives with these
measurements are to provide an alternative estimate of individual radon exposure, to estimate the
radon exposure when no other data are at hand and to evaluate the usefulness of RETRO
measurements.
For this study we followed a pre-determined plan which gives guidance on how to choose the
objects, what information should be noted etc. The objects chosen for RETRO measurement were
personal objects, which had been in the person's possession for more than 20 years. If possible,
two different objects were measured for each individual. In addition, a contemporary radon
measurement was undertaken during the three-month period during which the RETRO
measurement was made.
Of the 419 persons contacted, we made at least one RETRO measurement for 344 of them, 9% had
no suitable object and 9% refused to allow measurements. A total of 576 different objects were
found and 568 were measured. For 225 persons we measured two personal objects that had been in
the same person's possession for more than 20 years. The standard deviation of the estimated mean
radon concentration obtained from these two objects had a median value of 13 Bq/m³ indicating a
precision of exposure estimation of about 20 %.
The correlation between 210 Po surface activity measured earlier and mean values of measured
radon concentrations in a number of Swedish dwellings is applied to estimate the historical
average radon concentration. This average correlation factor seems also to be valid for the
measurements in the non-smoker epidemiological study.
Measurement of surface implanted 210 Po activity in personal objects can provide information on
individual radon exposure which is of value in a radon epidemiological study. Additional
information using room-models will improve the accuracy of the assessed exposure.