[ RadSafe ] More about CT scan review article

[Steven Dapra]

Dec. 2

In their review article in the New England Journal of Medicine (11-29-07) 
about the purported dangers of cancer as a result of CT scans, Drs. Brenner 
and Hall write, "Depending on the machine settings, the organ being studied 
typically received a radiation dose in the range of 15 millisieverts (mSv) 
(in an adult) to 30 mSv (in a neonate) for a single CT scan, with an 
average of two to three CT scans per study.  At these doses, as reviewed 
elsewhere, [24] the most likely (though small) risk is for 
radiation-induced carcinogenesis."  (p. 2280, col. 1)

         Footnote 24 is a paper ("Cancer risks attributable to low doses of 
ionizing radiation: assessing what we really know") published in the 
Proceedings of the NAS in 2003, and written by DJ Brenner (yes, that 
Brenner), R Doll, and DT Goodhead.

         They next acknowledge their reliance on the atomic bombing data, 
noting that the bombing exposure was a "fairly uniform" whole body 
dose.  They then write, "There was a significant increase in the overall 
risk of cancer in the subgroup of atomic-bomb survivors who received low 
doses of radiation, ranging from 5 to 150 mSv [27-29]; the mean dose in 
this subgroup was about 40 mSv, which approximates the relevant organ dose 
from a typical CT study involving two or three scans in an adult."  (p. 
2280, cols. 1-2)

         Footnotes 27-29 refer to three papers in Radiation Research, 
published in 2003, 2000, and 2007 (in order by footnote).  A DL Preston was 
the lead author on fns. 27 and 29, and was the second of two co-authors on 
fn. 28.

         Brenner and Hall next invoke "a recent large-scale study of 
400,000 radiation workers in the nuclear industry [30, 31] who were exposed 
to an average dose of approximately 20 mSv (a typical organ dose from a 
single CT scan for an adult).  A significant association was reported 
between the radiation dose and mortality from cancer in this cohort (with a 
significant increase in the risk of cancer among workers who received doses 
between 5 and 150 mSv);"  (p. 2280, col. 2)

         Footnotes 30 and 31 refer to papers by the same three authors 
published in Radiation Research in 2007; and in the British Medical Journal 
in 2005.  I took a cursory look at the latter paper and found that the 
authors did not correct for smoking.  They said that smoking was roughly 
equated with socio-economic status and that they had corrected for this, 
thus partially compensating for smoking.

         Brenner and Hall note the increased radiosensitivity of children, 
and write, "In summary, there is direct evidence from epidemiologic studies 
that the organ doses corresponding to a common CT study (two or three 
scans, resulting in a dose in the range of 30 to 90 mSv) result in an 
increased risk of cancer.  The evidence is reasonably convincing for adult 
and very convincing for children."  (p. 2280, col. 2)

         Brenner and Hall next acknowledge that no "large-scale 
epidemiologic studies of the cancer risks associated with CT scans have 
been reported" but that one is just beginning.  For this, they cite the 
article "Study warns of 'avoidable' risks of CT scans," in Nature 
(2004;431; 391).  This is a half-page "News" article in Nature (23 Sept. 
2004), that begins by reporting on Brenner's contribution to a Sept. 7 
London conference on childhood leukemia.  The article mentions a 
co-authored study by Brenner and D. D. Elliston in Radiology (2004) on the 
risks of adult full-body CT scans.  It mentions a straw poll taken at a 
2001 radiology conference saying that delegates believed that up to 30 
percent of pediatric CT scans were unnecessary (Pediatric Radiology, 
2002).  The article also notes two occasions wherein lower doses of 
radiation were recommended in CT scans of children.  The last paragraph of 
the article says, "A proposed epidemiological study by researchers at the 
University of Newcastle upon Tyne, UK, may provide better data on the risks 
[of CT scans on children].  Mark Pearce and Louise Parker hope to study the 
hospital records of 100,000 children who received scans.  But Pearce 
cautions that several such studies will be needed to properly assess the 
risk of CT scans."

         Returning to Brenner and Hall, they say, "Although the results of 
such studies will not be available for some years, it is possible to 
estimate the cancer risks associated with the radiation exposure from any 
given CT scan [20]", and apply the bomb survivor data.  (p. 2280, col. 
2).  Footnote 20 is a paper in the American Journal of Roentgenology 
(2001).  It was co-authored by Brenner and Hall; by a D. Elliston (probably 
the D. D. Elliston who co-authored the study in Radiology mentioned in the 
preceding paragraph); and by W. Berdon.  Elliston and Berdon are at 
Columbia, as are Brenner and Hall.

         On pp. 2280-2281 Brenner and Hall write that CT-related risks from 
organ exposure can be directly assessed from epidemiologic data without 
extrapolating measured risks to lower doses.  This is footnote 33, a 2001 
paper in Medical Physics by the same co-authors of the Roentgenology paper 
in the preceding paragraph.  The Brenner and Hall New England Journal of 
Medicine review article has 46 footnotes.  Seven of them are to papers 
written or co-authored by Brenner or Hall or Elliston or Berdon.

Steven Dapra
sjd at swcp.com

Anyone wanting citations to any of the papers cited in this message may 
contact me and I will provide them.