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Despite Advances In The Accuracy Of CT Colonography In Detecting Polyps, Digestive Health Experts Urge Patients To Consider Risks And Realities
Findings from a
trial of the accuracy of CT colonography (CTC) compared to complete
colonoscopy in detecting large pre-cancerous polyps and colorectal cancers,
coordinated by the American College of Radiology Imaging Network (ACRIN),
raise several important issues for the public about colorectal cancer
screening using a CT scan of the abdomen: the potential need for follow-up
with complete colonoscopy in many cases, the real risk of undetected and
unreported smaller growths with pre-cancerous potential, the reality of
radiation risks relating to CT scans, as well as questions regarding
patient acceptability of this test.
"Today's findings underscore the reality that many patients who have
polyps detected by CT colonography will still have to undergo complete
colonoscopy," explained Dr. Amy Foxx-Orenstein, D.O., FACG, President of
the American College of Gastroenterology. Researchers found that as many as
12 percent to 17 percent of study participants screened by CTC would have
to be referred for complete colonoscopy depending on the size threshold for
reporting lesions in the colon. Of more significant concern, is that the
researchers only reported growths in the colon 5 mm or larger, leaving
unreported and therefore undetected an untold number of potentially high
risk pre-cancerous growths.
"The College sees significant strengths in the proven benefits of
visualizing pre-cancerous growths and removing them in a single examination
during colonoscopy," commented Dr. Foxx-Orenstein.
"There is a tremendous body of evidence that shows that clearing the
colon of polyps, including small polyps, significantly reduces colorectal
cancer mortality. Because of its excellent sensitivity in detecting polyps
and its potential for removing them and breaking the sequence of polyp to
cancer in a single diagnostic and therapeutic intervention, complete
colonoscopy is one of the most powerful preventive tools in clinical
medicine. Until a radiographic test can meet that standard,
gastroenterologists will continue to champion the lifesaving potential of
colonoscopy," Foxx-Orenstein added.
Evaluating the Potential of CT Colonography - What Patients Should Know
When evaluating new potential screening technologies, including CT
colonography, the ACG has focused its evaluation on several pieces of
evidence including: sensitivity for identification of polyps of various
sizes, standards for polyp removal, correlating patient risks (in this case
from radiation exposure), frequency of exams and the economic impact to the
healthcare system of separate diagnostic and therapeutic exams.
If all patients with a lesion measuring 5 mm or more on CT colonography
in this study were referred for complete colonoscopy, the
colonoscopy-referral rate would be 17 percent. In earlier findings by Dr.
Pickhardt and his colleagues in 2004, at least 30 percent of patients
undergoing virtual colonoscopy required conventional colonoscopy to remove
polyps 6 mm or larger.
Radiation Risk
The issue of radiation exposure risk are long-term and lifetime risks.
The results of the impact of patients undergoing CT and other radiologic
exams for a variety of reasons will not be known for some time. With a
proposed screening schedule of five years or less for CTC, depending upon
the findings, the cancer risks from the CTC test itself are not
insignificant. Although it is a challenge to define precise risk estimates
related to low doses of radiation exposure, the ionizing radiation exposure
from a single abdominal or chest CT may be associated with elevated risk
for DNA damage and cancer formation. X-rays used in medical diagnostic
procedures is the largest man-made source of radiation exposure to the
population contributing some 14 percent of the total annual exposure from
all sources. The U.S. Food and Drug Administration considers x-ray as a
carcinogen.
Patient Acceptability
Patient acceptance is another key factor in evaluating the promise of a
new technology. ACG notes that the CTC technology requires the same bowel
preparation as complete colonoscopy. There is also evidence that due to the
insertion of a tube in the rectum and insufflation of the abdomen with air
or gas, the patients, who are not sedated and awake, tend to feel
discomfort.
"It is important for patients to understand that CT colonography does
not at present represent a painless or risk-free procedure, nor does it
eliminate the need for bowel cleansing which patients report as a barrier
to screening," explained Dr. Foxx-Orenstein.
Moreover, the American Cancer Society recently issued a Multi-Society
Task Force Guideline on Colorectal Cancer which stated a preference for
tests which prevent colorectal cancer. According to the American College of
Gastroenterology, colonoscopy remains the preferred strategy for colorectal
cancer screening and prevention. Three studies have shown that colonoscopy
prevents about 80 percent of colorectal cancers from developing by removing
pre-cancerous polyps.
"The public should recognize that there is no evidence that any
radiographic test, including CT colonography, prevents the development of
colorectal cancer," said Dr. Foxx-Orenstein.
American College of Gastroenterology
http://www.acg.gi.org
În ciuda progreselor exactitatea CT în detectarea Colonography polipi, digestive Sãnãtate Exper Urge Pacienþii sã ia în considerare riscurile ºi realitãþi - Despite Advances In The Accuracy Of CT Colonography In Detecting Polyps, Digestive Health Experts Urge Patients To Consider Risks And Realities - articole medicale engleza - startsanatate