Answer to Question #4150 Submitted to "Ask the Experts"

I worked for an oil company and had to be exposed to radioactive sources (cesium-137, americum-34). My readings of total effective dose are 2001: 0.009 rem; 2002: 0.64 rem (mostly in a short period of time, about two hours); 2003: 0.05 rem. I have been diagnosed with chronic myeloid leukemia. I wonder if the radiation might have an influence on the development of this disease? I know that the radiation levels are below the threshold (occupational dose) but I have read that leukemia does not have a linear dose response. I also read the "UNSCEAR 2000 report, Biological Effects at Low Radiation Doses." The hypothesis implies that the risk of cancer increases (linearly) with increasing exposure and that there is no threshold. As you can see I am confused because the International Commission on Radiological Protection threshold for occupational dose is 5 rem, but there is a lot of literature that mentions risk at lower radiation levels and even that there is no threshold. Could you help me to clarify this? Could radiation exposure increase the risk of developing leukemia even at low levels?

It is virtually impossible that your radiation exposure in recent years could be related to your present leukemia.  There are two reasons:

1. Your radiation dose has been quite small. The National Council on Radiation Protection and Measurements (NCRP) has estimated that the average American receives a dose of 0.3 rem per year from natural environmental sources. The NCRP further has recommended a dose limit for persons occupationally exposed to radiation of 5 rem in any year, with a limit of accumulated dose equal to the person's age expressed in rem. There is no confirmed evidence that any person has ever been harmed by doses of the magnitude you received.
    
2. The latent period for development of leukemia to the point that it can be detected is at least five years. In all studies of irradiated human populations, any leukemia detected within five years of exposure is regarded as having been present but undetectable when exposure occurred. The period at major risk, as determined from studies of the Japanese atomic bomb survivors and other populations, is five to 25 years after exposure, with occasional cases occurring later.

S. Julian Gibbs, DDS, PhD