  While radioactive sources used in medical diagnosis do not pose a great
security risk due to their low level of radioactivity, therapeutic sources are
extremely radioactive and can presumably be used as a radiological weapon.
Cobalt-60 and Cesium-137 sources are the most common ones used in radiotherapy
with over 10,000 of such sources currently in use worldwide, especially in the
developing world, which cannot afford modern accelerators. The present study
uses computer simulations to investigate the effects of using Cesium-137
sources from teletherapy devices as a radiological weapon. Assuming a
worst-case terrorist attack scenario, we estimate the ensuing cancer mortality,
land contamination, evacuation area, as well as the relevant evacuation,
decontamination, and health costs in the framework of the linear risk model.
The results indicate that an attack with a Cesium-137 dirty bomb in a large
metropolitan city (especially one that would involve several teletherapy
sources) although would not cause any statistically significant cancer
mortality current radiation safety standards would impose the evacuation of
large areas and the relocation of thousands of people.
