RE: Excess Absolute Risk (EAR)

["Fulmer, Philip" <FulmerP@ttnus.com>]

Mike,

I haven't seen the WHO report, but I can fax you a few pages from NCRP
80 if you like.  The NCRP does present the annual number of 2.5 per Gy
per year.  In their report, however, the NCRP multiplies this risk by
something called "years at risk."  In this context, "years at risk" is
not related to the exposure scenario but rather to the committed risk as
a function of time following a single exposure.  It's a combination of
the latency period for thyroid cancer and the expected lifespan of the
individual, age of the individual at exposure, etc., etc.  So it's more
a way to account for differences in committed risk if a person is
exposed later in life rather than sooner (since people later in life are
not generally as likely to live for 40 or 50 years following exposure).

What was intended by the WHO with a statement of "if this risk persists
unchanged..." is not entirely clear to me.  The risk is what it is and
is set when the dose is received.  Maybe the WHO was trying to be
delicate instead of saying "if the exposed population lives for 40 years
after the exposure."

Best regards,

Philip 
________________________
Philip C. Fulmer, PhD, CHP
TetraTech NUS
900 Trail Ridge Road
Aiken, SC 29803
(803) 649-7963
fulmerp@ttnus.com


-----Original Message-----
From: Mike Lantz [mailto:mlantz33@cybertrails.com]
Sent: Wednesday, February 03, 1999 10:38 PM
To: Multiple recipients of list
Subject: Excess Absolute Risk (EAR)


I'd like some help in understanding a risk term presented in a World
Health Organization (WHO) draft document on KI guidance.  They say it
comes from NCRP 80, which I couldn't find today.  The WHO took what they
describe as an external radiation risk term, Excess Absolute Risk (EAR),
and used it to calculate risk from internal exposures related to any
nuclear accident; like Chernobyl thyroid cancers in children.  The
problem I have, or question, is that this term was listed as 2.5 E-4 per
Gy per year.  They then say that "if this risk persists unchanged for 40
to 50 years, the lifetime risk of cancer would be 1% per Gy".  They
multiplied by 40 years to determine the total risk of thyroid cancers to
children.  

Does that make any sense that you would assume an unchanged risk for 40
years following a nuclear power plant accident?  Or am I not
understanding this EAR term?  

This isn't critical because we found an excellent document on the
subject of KI, NUREG-1633, filled with wonderful insights by HPs such as
Charlie Willis.  But I'd still like to understand the WHO's thinking
here.

Thanks in advance.

Mike Lantz, CHP
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html