Another Side Dish For RIBs & BEIR - Fetal Case Study

You need not read this to follow the RIBs & BEIR series, this just provides a sidebar.

I created a link to NRC Event Reports on the Home page.  If you click on it today (11/04/11), you will see there was an incident involving a fetus that received an estimated 17.4 rads.

Since we've been discussing cancer and the BEIR VII report, I thought this case would provide further insight.

From basic radiobiology we know the fetus is more radiosensitive than an adult.  This is because most of its cells are undergoing rapid growth and differentiation.

We might be tempted to use the BEIR VII cancer risk estimate and apply it here, but we can't.  BEIR VII didn't include the fetus.

The EPA (2008) recognized this shortfall and estimated a risk coefficient of .04/Gy (see page 96) for childhood cancer from fetal radiation exposure . 

We really shouldn't apply this risk coefficient without fully understanding how the exposed fetus (in the NRC report) might differ from those considered in developing the risk coefficient.  But since this is just a blog, and I'm trying to pull a number of points together, let's just assume the event report fetus is well represented.

Then: (17.4 rads) x (1Gy/100 rads) x (.04/Gy) = 0.7%

Note:  this is the increased risk of getting childhood cancer. To calculate the risk of getting cancer into adulthood, one would need to look at the epidemiological table, matched for sex, which assumes an exposed age of 0, and gives an attained age of X (where X is the age under being contemplated., ie chance of getting cancer by age 50 or 70).