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Acticle: Lung cancer screening raises lung cancer risk
The original article can be found at
http://www.auntminnie.com/default.asp?Sec=sup&Sub=cto&Pag=dis&ItemId=62046
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Hiroshima revisited: Lung cancer screening raises lung
cancer risk
6/14/04
By: Eric Barnes
Depending on where one stands in the radiation
hormesis debate, a new study on CT lung screening may
or may not be of concern. Still, new estimates of a 5%
increase in excess lung cancers among frequently
screened smokers are noteworthy in anyone's book, and
may even prompt some radiologists to fine-tune their
protocols.
"The potential benefits of lung cancer screening have
been much discussed, as have the potential risks of
invasive procedures from false-positive findings,
wrote David Brenner, Ph.D., DSc, in Radiology. "Less
attention has been paid to the potential radiation
risks -- specifically radiation-induced lung cancer --
associated with CT lung screening. In part this is
because the screening technique involves 'low-dose'
rather than standard CT lung scans, and in part
because excess relative risks of radiation-induced
cancer generally decrease markedly with increasing
age" (Radiology, May 2004, Vol. 231:2, pp. 440-445).
However, Brenner cited a number of considerations
suggesting that the risk of lung screening may not be
negligible. First, assessments of the interaction
between radiation and smoking have shown that cancer
risks are generally multiplicative of background
cancer risk, which obviously applies to a screening
population of smokers and former smokers. Second,
radiation-associated risks do not appear to decline
with age for lung cancers as they do with other forms
of the disease.
Finally, the well known atomic bomb survivor data from
Hiroshima are directly applicable to lung cancer
cases, and in comparable doses, Brenner stated.
"For example, 10 low-dose CT lung screening
examinations would produce lung doses in the range of
25 to 90 mGy," he wrote. "Among approximately 30,000
individuals in the cancer incidence cohort of atomic
bomb survivors who received doses between 5 and 100
mSv (mean dose, 29 mSv), there was a statistically
significant increase in cancer risk (77 excess
cancers, p = 0.05) compared to that in the control
population."
In his report, Brenner derived the dose-, sex-, and
smoking status-dependent excess relative risks of lung
cancer from cancer incidence data for atomic bomb
survivors, and then calculated the excess lung cancer
risks associated with a single CT lung examination at
a given age in a U.S. population. From these he
calculated the overall risks associated with annual CT
lung screening, the goal of most current trials.
According to this calculation, the estimated lifetime
excess relative risk for a 50-year-old female smoker
who receives a typical 5.2 mGy dose in CT lung
screening is 0.0037. The estimated age-shifted
background lifetime lung-cancer risk is 0.16, the
estimated probability of surviving at least 10 years
is 0.96, and thus, the estimated excess lung cancer
risk due to the single CT exam is 0.00057.
However, were the same 50-year-old woman to continue
annual screening through age 75, she would accrue an
estimated excess lung cancer risk of 0.85% (95% CI:
0.28%, 2.2%) associated with the total radiation
exposure, not including the expected lung cancer risk
of 16.9%. For a 50-year-old male smoker, the
accumulated excess risk is 0.23% (95% CI: 0.6%.
0.63%), not including an expected lung cancer risk of
15.8%.
"If the entire U.S. population of current and former
smokers aged 50-75 years -- approximately 36 million
people -- were offered annual CT lung screening until
age 75, with a 50% compliance rate, the estimated
number of lung cancers associated with the radiation
from these examinations would be about 36,000 (95% CI:
11,300, 93,600)," the author wrote. "Of the
approximately 18 million people older than 50 years
who would undergo annual screening until age 75, about
1.9 million would be expected to contract lung cancer
independent of the CT lung radiation dose; thus, the
radiation exposure from annual CT lung examinations
would increase this number by approximately 1.8% (95%
CI: 0.5%, 5.5%)."
The estimate drops from 36,000 to 6,000 cancers if
screening starts at age 60 rather than 50, an increase
in incidence of approximately 0.8%.
The author also explained why he estimated radiation
risks for radiation-induced lung cancer incidence
rather than mortality. Given the high
mortality-to-morbidity associated with lung cancer, he
wrote, incidence risks seemed reasonable.
"Given the estimated upper limit of a 5.5% increase in
lung cancer risk due to annual CT-related radiation
exposure, a mortality benefit of considerably more
than 5% may be necessary to outweigh the potential
radiation risks," he wrote. "If the radiation risks
prove to be a concern, an increase in the minimum age
at which screening is recommended, from 50 to 60
years, would reduce the risks considerably. Another
alternative would be to screen every two years, which
would reduce the radiation risk by about 50%."
By Eric Barnes
AuntMinnie.com staff writer
June 14, 2004
Related Reading
Utility of CT screening for lung cancer remains
unproven, June 1, 2004
CAD gets role in new ELCAP lung study, April 29, 2004
Radiologists offer new guidance on reducing CT
radiation dose, August 14, 2003
Radiation doses in Hiroshima survivors confirmed, July
31, 2003
Radiation hormesis and the radiologic imperative,
March 21, 2003
Studies cast doubt on low-level radiation dangers,
January 30, 2003
Copyright © 2004 AuntMinnie.com
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John Jacobus, MS
Certified Health Physicist
e-mail: crispy_bird@yahoo.com
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