[ RadSafe ] Study evaluates radiation dose, cancer risk for whole-body PET/CT

Brennan, Mike (DOH) Mike.Brennan at DOH.WA.GOV
Wed May 14 13:22:51 CDT 2008

I am not a PET/CT kind of rad guy, but this study seems to miss an
extremely important point, and that is what is the life expectancy of
the individual involved, both with and without the procedure?  If the
person is going to die in the short-term without the information from
the scan, then there is no long-term health risk.  If the procedure has
been properly called for by the medical professionals, then it is
reasonable to assume that the patient's overall risk is decreased by
orders of magnitude, regardless of the theoretical increased risk of

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Sent: Tuesday, May 13, 2008 5:09 PM
To: radsafe at radlab.nl
Subject: [ RadSafe ] Study evaluates radiation dose,cancer risk for
whole-body PET/CT

Study evaluates radiation dose, cancer risk for whole-body PET/CT By
Wayne Forrest AuntMinnie.com staff writer May 9, 2008

 A new study from Hong Kong suggests that whole-body PET/CT scans and
excessive radiation doses can increase the risk of cancer, especially
among young patients and women.
The research from the University of Hong Kong and Queen Mary Hospital in
Hong Kong also offers effective CT radiation doses for men and women, as
well as effective doses for combined PET/CT procedures.
PET/CT "has a very important role in oncology and infection, and its
role has been expanding," said Dr. Bingsheng Huang from the University
of Hong Kong's Department of Diagnostic Radiology and Department of
Clinical Oncology. "However, it has increased patient radiation exposure
and this radiation has a well-known, adverse effect on patients" with a
greater cancer risk.
The purpose of the study, presented at the 2008 American Roentgen Ray
Society (ARRS) meeting in Washington, DC, was to estimate the radiation
dose of an adult whole-body PET/CT with a diagnostic CT scan and
clinically evaluate the cancer risk to the Hong Kong population caused
by the radiation exposure.
Researchers analyzed whole-body FDG PET/CT scans from vertex to midthigh
acquired on a Discovery PET/CT system from GE Healthcare of Chalfont St.
Giles, U.K. The hybrid scanner is equipped with 64-slice CT technology,
and the injected dose of F-18 FDG was assumed to be 370 MBq. Direct
measurements of CT scan dose were performed on a standard phantom
equipped with 314 thermoluminescent dosimeters. 
The lifetime attributable risk (LAR) of cancer incidence was used to
estimate the excessive risk caused by the radiation of a PET/CT scan.
The study's source for that data was the "Health Risks from Exposure to
Low Levels of Ionizing Radiation: BEIR VII Phase 2" report, published by
the National Academy of Sciences in Washington, DC, in 2006. Researchers
used the information to create a model to calculate the lifetime
attributable risk for the Hong Kong Chinese population.
"In this (BEIR) report, each organ's cancer risk is given and each organ
cancer risk is calculated for a special radiation dose," Huang said in
his presentation. "The whole-body cancer risk can be acquired by summing
up each organ's risk."
The researchers found that the effective radiation dose for a CT scan is
7.22 mSv for women and 7.42 mSv for men. The effective dose for a PET
scan was calculated to be 6.23 mSv for both women and men. Huang noted a
high radiation PET dose of 59.20 mSv in the bladder, attributing the
finding to the accumulation of FDG in the bladder.

Chart courtesy of Dr. Bingsheng Huang, University of Hong Kong, ARRS
2008 presentation. 
Subsequently, the total combined effective radiation dose for PET/CT is
13.45 mSv for women and 13.65 mSv for men.
Using the LAR model, the researchers also calculated the cancer risk for
men and women between the ages of 20 and 80 years. "For males, the
cancer risk is from 0.33% to 0.09% (per 100,000 men). For females, it is
from 0.40% to 0.11% (per 100,000 women)," Huang said. "We can see that
the cancer risk increased when the exposed age decreased, and the
females' cancer risk is always higher than males'."

Chart courtesy of Dr. Bingsheng Huang, University of Hong Kong, ARRS
2008 presentation. 
The researchers calculated that the cancer incidence induced by one
whole-body PET/CT scan contributes approximately 1% to 2% to total
lifetime cancer incidence. Given this finding, Huang said that the
radiology community should be mindful of the situation and clinically
justify the use of PET/CT on patients.
The researchers further recommended that "modification of scanning
protocols tailored to the specific clinical indication should be
considered, so as to balance between good image quality and reduced
radiation dose exposure."
By Wayne Forrest
AuntMinnie.com staff writer
May 5, 2008

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