In the November 29, 2007, issue of the New England Journal of Medicine, Drs. Brenner and Hall of the Center for Radiological Research, Columbia University Medical Center, New York, discuss the implications of the rising use of Computed Tomography (CT) scanning in the United States. “The widespread use of CT represents probably the single most important advance in diagnostic radiology.” Nonetheless, CT does involve radiation, so it should be used with caution.

They point in particular to the sharp rise in the use of CT for diagnosing children, and for full-body scanning of asymptomatic adults. These two applications in particular are causes for concern. Some doctors are suggesting to use full-body CT instead of an annual office exam, which the authors feel is an unwarranted risk.

“The situation is even clearer for children, who are at greater risk than adults from a given dose of radiation, both because they are inherently more radiosensitive and because they have more remaining years of life during which a radiation-induced cancer could develop.”

According to this article, for a 30-year-old person, the lifetime risk of developing a cancer as a result of a single CT scan is estimated to be 0.02% (two hundredths of one percent). Risks are higher for children, lower for older people.

In 1996 it was estimated that approximately 0.4% (less than half of one percent) of all cancers in the United States occurred as a result of CT use. With the increased use of CT scanning we see today, and factoring in estimates of future use heavily influenced by new programs to do full-body scans yearly, they estimate that in the future, as much as 2% of all cancer in the U.S. may be attributable to CT.

The press, of course, has focused on this 2%, misquoting the article widely as having declared that 2% of all cancers are now caused by CT. That is NOT what this article is saying. The authors are trying to limit the unnecessary use of CT. At the same time, they applaud the use of CT as a diagnostic tool for good medical reasons, including the preventive scanning of individuals at risk, as recommended in the VHLFA screening protocol.

The authors point out that many doctors were unaware, or at least not thoughtful about the fact that CT involves radiation exposure. Problems also arise “when CT scans are requested in the practice of defensive medicine, or when a CT scan, justified in itself, is repeated as the patient passes through the medical system, often simply because of a lack of communication. Tellingly, a straw poll of pediatric radiologists suggested that perhaps one-third of CT studies could be replaced by alternative approaches or not performed at all.” [p.2282].

“From an individual standpoint, when a CT scan is justified by medical need, the associated risk is small relative to the diagnostic information obtained. However, if it is true that as many as one-third of all CT scans are not justified by medical need, and it appears to be likely, perhaps 20 million adults and, crucially, more than one million children per year in the United States are being irradiated unnecessarily.” [p.2283]

The bottom line is that the guidelines in the VHL Handbook are still on target. For children, we recommend screening methods that avoid radiation. Once you have a diagnosed problem that requires careful following, MRI would generally be preferred unless CT is deemed medically necessary.

We asked two radiologists to comment on this story:

– from Peter Choyke, M.D., U.S. National Cancer Institute, Bethesda, Maryland

We speculate about the effects of radiation at the doses/frequency of clinical imaging. But no one can put a number to it, even in the general population, let alone in an individual patient. At the same time, there are real, quantifiable problems from not making a proper diagnosis in a VHL patient. This is the same dilemma we have always had since we started advocating routine imaging. I think the balance still comes down clearly in favor of imaging rather than holding back in VHL patients.

-- from Richard Cohan, M.D., Abdominal Radiology, University of Michigan, Ann Arbor, Michigan:

I don’t think that this changes anything for the VHL patients. As per my lecture this past June, there are some risks related to radiation (although the risks being quoted may be a little overstated). There are radiation exposure risks to airplane flight, too.

In a VHL patient it is tremendously more important to use CT to detect and monitor small tumors. The risk of not imaging someone and allowing a renal or pancreatic tumor to grow uncontrollably is not acceptable. The likelihood of an unmonitored VHL tumor developing into a cancer is very high. I would encourage you to encourage your readers to relax. The message in all this is to eliminate unnecessary imaging.

As for gadolinium contrast in MRI, we are still learning; however, the news is encouraging. Just by being more cautious and by altering some of the agents we use in some instances, many centers have drastically reduced their number of cases of Nephrogenic Systemic Fibrosis (NSF). Some (including ours and one of the hospitals in Denmark that first reported the association) have virtually stopped seeing NSF cases in the past year.

For following tumors, either CT or MRI is acceptable, although I personally would skew toward MRI in younger patients (under the age of 40, say), if they have good kidney function. CT or MRI are fine to image older patients.

In young or older patients with severe renal failure, MRI is still probably safer than CT (which can damage the kidneys further if a patient is not on chronic dialysis); however, it might be reasonable to consider MRI without contrast first or to use one of the gadolinium agents that has not yet been seen to cause NSF.

Young or old patients on long-term dialysis should probably be followed with CT instead of MRI.

References: Brenner D and Hall E, Computed Tomography: An Increasing Source of Radiation Exposure, New England Journal of Medicine 2007; 357:2277-84. PMID: 18046031

Dr. Cohan’s talk from the Boston meeting is reported in the September newsletter. The full DVD and handout are available at http://vhl.impactlearning.org

As printed in the VHL Family Forum 16:1, January/February 2008. For permission to reprint, please contact VHL Family Alliance, editor@vhl.org.