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Old 12-01-2010, 01:04 AM
Dross Dross is offline
Join Date: Nov 2006
Posts: 883
Default Cancer risk from medical radiation may have been overestimated

The risk of developing radiation-induced cancer from computed tomography (CT) may be lower than previously thought, according to a study presented today at the annual meeting of the Radiological Society of North America (RSNA).

"Radiation from medical imaging has gotten a tremendous amount of attention in recent years," said Aabed Meer, an M.D. candidate at Stanford University in Palo Alto, Calif. "This is one of the first studies to track CT utilization in such a large population."

The researchers conducted a retrospective study using Medicare claims from 1998 through 2005 to analyze the distribution of CT scans, determine the ionizing radiation exposure associated with the exams and estimate the associated cancer risk in a population of older adults.

"The study focused on the elderly Medicare population, which receives the highest amount of per capita radiation," Meer said. "We analyzed more than 10 million records from the Medicare claims database."

The data were studied in two groups, including 5,267,230 records from 1998 through 2001 and 5,555,345 records from 2002 through 2005. For each group, the researchers analyzed the number and types of CT scans that each patient received to determine the percentage of patients exposed to "low" radiation doses of 50 millisieverts (mSv) to 100mSv and "high" radiation doses, in excess of 100mSv. They then used standard cancer risk models to estimate the number of cancers induced.

CT scans of the head were the most common examinations, representing 25 percent of the first group and 30 percent of the second group. However, abdominal CT delivered the greatest proportion of radiation, accounting for approximately 40 percent of the total radiation exposure in each group. Imaging of the pelvis and chest represented the second and third largest sources of radiation.

From 1998 to 2001, 42 percent of patients underwent CT scans. From 2002 to 2005, 49 percent of patients underwent CT scans. The percentage of patients exposed to radiation doses in both the low and high ranges approximately doubled from the first group to the second group. The researchers found this to be consistent with the increasing use of high-speed CT in patient diagnosis and management.

Cancer incidences related to ionizing radiation from CT were estimated to be 0.02 percent and 0.04 percent of the two groups, respectively.

"Our findings indicate a significantly lower risk of developing cancer from CT than previous estimates of 1.5 percent to 2.0 percent of the population," said coauthor Scott Atlas, M.D., chief of neuroradiology at the Stanford University Medical Center. "Regardless, the increasing reliance on CT scans underscores the importance of monitoring CT utilization and its consequences."

Last edited by gdpawel : 02-26-2013 at 05:03 PM. Reason: posted full article to forum board
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Old 10-16-2011, 02:04 AM
gdpawel gdpawel is offline
Join Date: Feb 2007
Location: Pennsylvania
Posts: 4,360
Default Hazards of CT scans

The Archives of Internal Medicine reported on two studies estimating that the radiation exposure from the 72 million CT scans ordered in 2007 alone will result in 15,000 additional cancer deaths twenty to thirty years down the road.

An editorial in the Archives pointed out that there is an eight-fold difference in CT scan use around the country with no better outcomes where more scans are done.

Is there evidence that a CT saves lives? No. No diagnostic/laboratory test ever has. This is not what it does.

Diagnostic/laboratory tests are judged by accuracy and reproducibility and never by their effect upon treatment outcomes. Most tests used today have comparable "sensitivities" and "specificities."

CT scans were not approved because they saved lives in a controlled clinical trial that compared the outcome of patients who received care with or without the benefit of a CT scan. They were approved because their performance characteristics (sensitivity/specificity) are reproducible, favorable and provide information to treating physicians.

In cancer medicine, no test in oncology has ever been shown in prospective randomized clinical trials to improve patient outcomes. The existing standard has always been the "accuracy" of the test. This is true for every single test used in cancer medicine, from estrogen receptors to panels of immunohistochemical stains (IHC) to diagnosing and classifying tumor to Her2/neu and CA-125 to cell culture assays to MRI's, CT Scans, Pet Scans and so on.

Even when you get to the new genetic/molecular tests, the validation standard that private insurance companies is accepting is "accuracy" and not "efficacy." The essential "proof" is that all they have to do for these tests is that the test has a useful degree of "accuracy," not that the use of the diagnostic test improves clinical outcomes.

A cardiac CT provides anatomic information regarding the presence or absence of blockages in coronary arteries. Such findings alone do not determine whether or not a patient requires an invasive procedure such as an angiogram or angioplasty/stent. Such decisions should be based on physiologic indicators such as presence of angina or, more importantly, an abnormal stress test. A cardiac CT by itself will never be proven to save lives. However, it is yet another tool in the arsenal that must be used properly.

In cancer medicine, the CT is used to follow the size of the patient's tumor while the patient is receiving repeated courses of chemotherapy to determine whether or not the treatment is working and whether or not different drugs should be given, instead. This is an entirely unproven benefit, and were appropriate studies ever to be performed, there wouldn't be any measurable benefit at all, in terms of improving patient response to chemotherapy or patient survival with chemotherapy.

CT Scans and Cancer Risk: Been There, Done That


Projected Cancer Risks From Computed Tomographic Scans Performed in the United States in 2007

These detailed estimates highlight several areas of CT scan use that make large contributions to the total cancer risk, including several scan types and age groups with a high frequency of use or scans involving relatively high doses, in which risk-reduction efforts may be warranted.


Radiation Dose Associated With Common Computed Tomography Examinations and the Associated Lifetime Attributable Risk of Cancer

Radiation doses from commonly performed diagnostic CT examinations are higher and more variable than generally quoted, highlighting the need for greater standardization across institutions.

Gregory D. Pawelski

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