Do cancers soar with CT scans?
Most CT scans result in limited exposure
Benefits from CT scans are not without risks
— Photo: Mohammed Yousuf
Useful tool: CT scans are immensely useful in diagnosis and in the guidance of therapeutic procedures.
Recently, Drs David Brenner and Eric Hall, researchers in the Columbia University Medical Centre, New York contended that about 0.4 per cent of all cancers in the U.S. may be attributable to radiation from computed tomography (CT) studies.
They claimed that they used the most scientific radiation risk estimates, and the data on the use of CT from 1991 to 1996.
If current data are used, it may be as high as 1.5 to 2 per cent, they reported in the New England Journal of Medicine (NEJM, November 29, 2007).
Low level radiation
The American College of Radiology (ACR), the Radiological Society of North America (RSNA) and the American Association of Physicists in Medicine (AAPM) reacted to the NEJM paper with predictable alacrity. The effect of low level radiation on living beings continues to be controversial (The Hindu, July 14, 2005).
ACR declared that certain conclusions and comparisons made in the NEJM study may be inappropriate and cause patients to mistakenly avoid getting life-saving medical imaging care.
“Patients need accurate information on which to base their healthcare decisions. They may be terribly confused and unduly distressed by some of the statements in this study,” Dr Arl Van Moore Jr., chairman of the ACR Board of Chancellors cautioned.
“The Brenner article illuminates many issues of importance in regards to CT, but the CT experts in the AAPM feel that much of the message of this article may be misconstrued or misunderstood by the press or by the public who may not be experts in CT,” AAPM warned.
“Advancing technology has increasingly allowed imaging exams to replace more invasive techniques, but has also resulted in increased radiation exposure for Americans” ACR conceded.
ACR and AAPM faulted the study for equating the survivors of atomic bombings to patients undergoing CT scans.
“Most CT examinations are conducted under controlled conditions. They result in limited radiation exposure to a small portion of the body.
Atomic bomb survivors experienced instantaneous radiation exposure to the whole body,” ACR clarified. There were other differences. Brenner and Hall argued that survivors of atomic bombings who received doses similar to patients undergoing CT scans did suffer excess cancers.
AAPM wanted that patients should discuss with their physicians not only the radiation risks of the CT examination, but the risks of not having the diagnostic information that CT provides.
AAPM acknowledged that David Brenner and Eric Hall are esteemed scientists and respected experts in radiation risk and AAPM’s release is in no way meant to impeach or undermine their impressive credentials.
Radiologists, medical physicists and other radiology professionals have long recognised the need to implement CT practice conscientiously and maintain rigorous standards of practice (RSNA, 2007).
The NEJM study focussed attention on overuse of CT. One million children and 20 million adults in the U.S. undergo unnecessary CT scan procedures annually.
Some researchers believe that estimating the number of cancers at low radiation doses has no scientific basis. Others like Brenner and Hall disagree.
But all agree on some key points. CT scans are immensely useful in diagnosing diseases and trauma and in the guidance of interventional and therapeutic procedures.
Not risk free
However, these benefits are not without risks. The individual risk from X-rays associated with a CT scan is quite small, compared to the benefits of diagnosis in medically needed procedures.
It is important to keep the radiation doses during medical X-ray procedures as low as reasonably achievable.
Using CT for routine screening is unjustified (The Hindu, January, 5, 2006). Specialists do not recommend CT coronary angiography of asymptomatic patients for assessing occult coronary artery disease (The Hindu, November 2, 2006).
Physicians must make every effort to reduce radiation dose in CT procedures, especially for children (The Hindu, February 8, 2007). CT should not be used to screen persons for lung cancer (The Hindu, September 13, 2007).
Specialist agencies across the board fear that the public may not understand complex scientific arguments.
Whether cancers soar with CT scans cannot be answered conclusively. Prudence demands caution in using this powerful medical imaging modality.
They tend to forget the fact that physicians face the challenge every day. The public will resolve the issues if specialists give all the inputs.
K.S. PARTHASARATHY Former Secretary, AERB
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