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Epidemiology and policy
P1-357 Statistical analysis of spatial survival data and its application to the cohort study of Hiroshima atomic bomb survivors
  1. T Tonda,
  2. K Satoh,
  3. K Otani,
  4. Y Sato,
  5. H Maruyama,
  6. H Kawakami,
  7. S Tashiro,
  8. M Hoshi,
  9. M Ohtaki
  1. Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima, Japan

Abstract

Introduction While there are considerable studies on the relationship between the risk of disease or death and direct exposure from the atomic bomb, the risk for indirect exposure caused by residual radioactivity has been ignored. One of the reasons is that risk assessments have utilised estimated radiation dose but it is difficult to estimate indirect exposure. To evaluate risks for indirect radiation exposure as well as direct exposure, we developed a statistical method that evaluates risk with respect to individual location at the time of atomic bomb exposure instead of radiation dose.

Methods Subjects for analysis were selected from the ABS database of the RIRBM at Hiroshima University. The number of death from all causes was 9641 and the number of censoring was 21 414. The follow-up period was from 1980 to 1997. Mesh coordinates of 100 m in width were used to define location. Sex and age at atomic bomb exposure were used as covariates. Applying the proposed method to the data, we estimated the location-specific risks for direct and indirect exposure.

Result and conclusion The contour of estimated risk showed that the north-west region has higher risk compared to other areas. The resultant risk map, excluding the risk for direct exposure, still has contours skewed towards the north-west direction. These suggest that there exists an impact on risk that cannot be explained by direct exposure. The shape of the risk map, which is skewed towards the north-west direction, might be due in part to Black Rain.

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