Monday, June 17, 2013

New Model for Assessment of Lung Cancer Incidence with Uranium Miners

 

by Peter Diehl
Prof. Wolfgang Jacobi, former director of the Institut für Strahlenschutz of the GSF external link - Forschungszentrum für Umwelt und Gesundheit GmbH (Institute for Radiation Protection of the GSF - Research Center for Environment and Health Ltd.) in Neuherberg, Germany, has analysed radiation exposure data of East Germany's uranium mining company Wismut, to find criteria for the recognition of lung cancers as occupationally caused or not. He developed a model that relates a lung cancer incidence to the work at Wismut for much lower doses than previously thought.  Since there is no personal data available on radon decay product exposure for the Wismut workers, general guidelines have to be found for the recognition of lung cancers as occupation related. During Wismut's early years 1946-1955, average annual exposure to radon daughters for miners is estimated at around 100-250 WLM (Working Level Month). This average exposure corresponds to radon concentrations in air of around 100,000 Bq/m3, while maximum radon concentrations reached 2 million Bq/m3. Between 1956 and 1970, radon daughter exposure strongly decreased, and since 1970 average annual exposure is around 4 WLM.

 Based on epidemiological data from uranium miner studies published in literature, Jacobi developed a ZSE (time since exposure)-model to determine the lung cancer rate depending on exposure, age at exposure and age at lung cancer incidence. Due to insufficient data, the model makes no difference between smokers and non-smokers.

The results of the model are discussed for the following cases:
  1. For miners who worked at least one year between 1946 and 1955 (and thus at least received around 200 WLM), the probability of causation for a lung cancer as occupation related is greater than 50%, independent of the age at lung cancer incidence.
  2. For miners who worked during five years between 1956 and 1960 and thus accumulated around 190 WLM, the probability of causation for a lung cancer as occupation related is greater than 50%, independent of the age at exposure and at lung cancer incidence.
  3. For those who worked during five years between 1961 and 1965 and thus accumulated around 90 WLM, the probability of causation for a lung cancer as occupation related is greater than 50% only, if lung cancer incidence was around 7-20 years after exposure.
  4. For those who worked during five years between 1966 and 1970 and thus accumulated around 30 WLM, the probability of causation for a lung cancer as occupation related is greater than 50% only, if the age at exposure was 20-40 and if lung cancer incidence was around 10-20 years after exposure.
  5. For those who worked since 1970 and thus accumulated around 4 WLM per year, the probability of causation for a lung cancer as occupation related is dependant on period of exposure, age at exposure and age at lung cancer incidence. For example:
    • After ten years of exposure and accumulation of 40 WLM, the probability of causation is only greater than 50%, if the age at exposure was 20 and the age at lung cancer incidence was 33-43, or if the age at exposure was 30 and the age at lung cancer incidence was 44-51.
    • After 30 years of exposure and accumulation of 120 WLM, the probability of causation is greater than 50%, if the age at exposure was 20 and the age at lung cancer incidence was 33-70, or if the age at exposure was 30 and the age at lung cancer incidence was 44-76.
With this model, the employers' liability insurance association, who has to pay for the compensation of occupationally caused diseases, has a first guideline for the assessment of lung cancers with Wismut miners.  A comparison of Jacobi's model with the BEIR IV model of 1988 is presented in [2]. It is worth noting that, according to this model, already an exposure of 30 WLM may be regarded as a cause of a lung cancer incidence, depending on age at exposure and age at cancer incidence.  According to recognition practice under the GDR-era, at least 150 WLM of exposure were necessary for recognition (during the early years, the limit even was at 450 WLM). With this limit, no worker had a chance for recognition, if he had worked for example only after 1970. With the new model, all cases of lung cancer that were not recognized, have to be reassessed.  It's also interesting to compare the results of this model to the regulations met in the US Radiation Exposure Compensation Act of 1990. According to the original version of this act, only those miners who worked between 1947 and 1971 and received at least 200 WLM (non-smokers), 300 WLM (smokers with incidence before age 45), 500 WLM (other smokers) and developed lung cancer or a nonmalignant respiratory disease, should receive compensation. In 2002, the exposure threshold was lowered to 40 WLM for all miners.

> Compensation of Navajo Uranium Miners
The model is available online in the Uranium Miner Health Risk Calculator. Sources:
[1] W.Jacobi, K.Henrichs, D.Barclay: Verursachungs- Wahrscheinlichkeit von Lungenkrebs durch die berufliche Strahlenexposition von Uran-Bergarbeitern der WISMUT AG, [Probability of causation for lung cancer due to the occupational radiation exposure of uranium miners of WISMUT AG], 67 pages in German, GSF-Bericht S-14/92, Neuherberg 1992.
Order address: GSF external link - Forschungszentrum für Umwelt und Gesundheit GmbH, Neuherberg, Ingolstädter Landstraße 1, D-85764 Oberschleißheim, Germany.
Tel. +49-89-3187-4011, Fax: +49-89-3187-3323 [2] Chmelevsky,D. et al.: Probability of causation for lung cancer after exposure to radon progeny: a comparison of models and data; in: Health Physics Vol.67, No.1, July 1994, p.15-23

http://www.wise-uranium.org/uhm.html#PULMFIBR