Geographical shielding of Nagasaki A-bomb exposure

This study was performed to collect data concerning the title in Old Nagasaki City for the future assessment of exposure effect on cancer mortality as there had been no such data in Nagasaki University. The City areas were classified in 237 regions shielded (45), partly shielded (41) and not-shielded (151) by hills surrounding the City along with the 5 steps of distances from <1.0 to 5 km or more from the hypocenter (503 m high) + Nishiyama region (shielded) with use of Using Arc View GIS (Geological Information System, USA). Cancer mortality in each region was studied on total 43,735 survivors directly exposed to A-bomb at the age of <30 y who had lived in the City on Jan. 1, 1970. Cancer death was studied on this cohort until Dec. 31, 2011 (during 42 years). Numbers of not-shielded people were estimated to be 8,779 (49.3%) males and 13,430 (51.8%) females. Curves vs time of their mortality per 100 thousands during the 42 years were found to have the peak of about 600 males exposed at 1.0-1.9 km from the hypocenter and about 350 females at <1.0 km. The higher was the mortality, the closer was the distance from the hypocenter. The correlation between the mortality and distance was thus found, but not in shielded people. The effect of this geographical shielding should be considered in assessment of Nagasaki A-bomb exposure. (T.T.)