COMMENTARY

April 2006: CT Scans and Cancer: How One Radiologist Is Safeguarding His Patients

Robert Chevrier

Disclosures

April 06, 2006

The CME/CE program below, which was developed for Medscape by Richard Semelka, MD, University of North Carolina, Chapel Hill, has awarded over 5000 credits to participants after only 1 month of publication:

Imaging X-rays Cause Cancer: A Call to Action for Caregivers and Patients
http://www.medscape.com/viewprogram/5063?src=hp8.cme

It's clear, both from the volume of emails dropped in my inbox and the tone of the communication, that Dr. Semelka has tweaked a chord.

To date, I have received more than 500 notes from patients requesting guidance and additional information concerning the potential dangers of CT radiation.

The reaction to the piece from the radiology community has been nothing less than astonishing. Either radiologists were totally unaware of the potential dangers of CT radiation or, with some exceptions owing to the belief that the reflexive use of CT scanning cannot be altered, are actively involved in their hospitals and communities in efforts to address this critical issue and preserve the safety of their patients.

A communication from Steven Birnbaum, MD, received via Dr. Semelka best illustrates how one caring clinician is attempting to tilt the CT radiation paradigm toward safer practices at his institution.

Dr. Semelka:

Enclosed are some thoughts prompted by your article outlining the potential radiation risks associated with CT scanning:

Radiation Safety for Clinicians

Helical (aka slip ring or multidetector) computed tomography (CT) has revolutionized diagnostic cross-sectional imaging by enabling the scanning of a volume of tissue instead of scanning the patient one slice at a time. This technology, combined with further advances in data handling, has allowed radiologists an unprecedented ability to image the body and reconstruct data in multiple planes with little loss of resolution in ever shorter times. New applications of this technology have become common in clinical use. Renal and ureteral stone studies, CT pulmonary angiography, and acute abdominal imaging have proven diagnostic utility. And, at the community hospital level, CT angiography of virtually any body part in 1 or 2 breath holds, including noninvasive coronary arteriography, is coming into its own.

It is important for us to recognize that, as in anything in medicine or life, this incredible technology comes with a price.

That price is increased radiation exposure.

Radiation and CT Scanning: What We Know

In the individual, elderly patient undergoing 1 or several CT studies, this is of no concern given the dosages and lag time of low-dose radiation-induced carcinogenesis.

Data regarding the effects of low-dose radiation come from several sources. One source is the atom bomb survivors whose dosage was estimated from their distance from the blast hypocenter. This is somewhat difficult to extrapolate to medical irradiation because it was a one-time exposure to mostly gamma and neutron irradiation. Nevertheless, there is a clear dose-related increase in carcinogenesis seemingly without threshold for these individuals. The second major dataset is more akin to medical exposure. This is a group of female patients in a tuberculosis sanatorium in Nova Scotia [Canada] who were subjected to weekly/monthly fluoroscopy to monitor their disease. In this group of patients, there was a clear dose-related carcinogenic effect in the form of thyroid and breast cancer, which was dose-related.

Regarding helical CT scanning, what is the actual radiation risk? We just don't know. We do know that the skin entry and equivalent radiation dosages associated with helical abdominal CT may approximate the radiation dose received at the lower exposure end of the atom bomb survivors who were at some distance from the hypocenter of both Hiroshima and Nagasaki [Japan]. An abdominal helical CT is the radiologic exposure equivalent of 250 chest x-rays or 15 KUBs.

We also know that with multiple helical CT studies, particularly of the abdomen and pelvis, that radiation dosages will clearly approach the radiation received by the atomic bomb survivors of Hiroshima and Nagasaki. We also know that chest CT scans, pulmonary CT arteriograms, and neck CT scans result in significant radiation exposure of the female breast and thyroid gland. Since pulmonary CT arteriograms are often ordered in female patients of reproductive age, radiation to the breast and thyroid gland may pose a significant lifetime risk of carcinogenesis. In addition, intravenous contrast may increase thyroid radiation absorption through increased attenuation from iodine concentration. In fact, a CT pulmonary arteriogram results in breast irradiation equivalent to 10-25 two-view mammography studies.

Kids in Peril

Moreover, we know that the risk of radiation carcinogenesis is 10-15 times greater for children than for adults. At Southern New Hampshire Medical Center [Nashua, New Hampshire] and Parkland Medical Center [Derry, New Hampshire] we have for the last several years minimized the pediatric radiation dosage for CT by limiting the technique to only those instances when it was necessary to obtain diagnostic imaging quality as recommended by the FDA [US Food and Drug Administration]. Other more subtle effects may also be the result of radiation exposure particularly in infancy. For example, an increase in mental retardation was seen in the atomic bomb survivors who were exposed in utero. A recent study from Sweden reviewed the cognitive ability of young men applying for the Swedish military who had been exposed to low-dose irradiation in infancy for cutaneous cranial hemangiomas. Brain dosage was estimated and correlated significantly with subsequent poor school performance, attendance, and cognitive ability. The dosages to the brain in this study are twice those of the average infant head CT scan. The authors of this study recommended that the risks and benefits of CT scans in minor head trauma, particularly in infancy, be reevaluated.

What is also clear is that there is an alarming lack of awareness on the part of both referring clinicians and radiologists regarding the CT radiation issue. A recent study from Yale University [New Haven, Connecticut] documents this from a busy teaching hospital. In this study, only 7% of patients were informed of radiation risk prior to helical CT. Only 22% of ED [emergency department] physicians reported that they had provided risk-benefit information to patients about helical CT. And 47% of radiologists in this study believed that helical CT did result in an increased risk of carcinogenesis, but only 9% of ED physicians and 3% of patients were aware that there may be an increased risk. None of the patients and few of the radiologists or ED physicians could give an accurate exposure estimate of an abdominal helical CT study.

Several examples from our hospitals:

  • A 14-year-old boy with metabolic abnormalities that cause him to make renal and ureteral stones. We became aware that he had had 14 renal stone CT scans over 4 years. Following consultation with our radiation physicist, it was recommended that he and his family seek genetic counseling due to an increased risk of carcinogenesis and the possibility of reproductive mutations. He is now managed with renal ultrasound and single-shot IVPs [intravenous pyelograms] in instances in which further imaging is necessary.

  • Young adults with Crohn's disease who will have a lifetime of this disease and who often have an abdominal CT ordered with every exacerbation. We have several patients under 35 years of age who have undergone 8-12 abdominal/pelvic CT studies.

  • Management of nonspecific acute abdominal pain in the young. We have one 49-year-old patient in our practice who has made frequent visits to the ED with abdominal pain. This patient underwent 8 abdominal CT scans in a 14-month interval, all of which were normal.

  • An 18-year-old woman who underwent 8 abdominal-pelvic CT studies, a head CT scan, a CT pulmonary arteriogram, and a lower extremity CT scan; all of these CT studies, which were normal, were ordered through the ED over a 6-year period. To quote our radiation physicist upon consultation, ". . . current literature would suggest that the level of radiation exposure received by J. will increase her risk of getting cancer. An approximation of risk estimate from the dose received is 1 of 200."

  • A 38-year-old man with a seizure disorder who has undergone 16 head CT studies over the last 6 years; all of these scans, which were normal, were ordered through the ED.

Of great concern is a previous example that befell the radiology community in the midportion of the 20th century, very early in the history of diagnostic imaging.

Thorotrast, a suspension of thorium dioxide, was used as a contrast agent from about 1930 until 1950. It was a superb intravenous contrast agent, with a very low incidence of immediate side effects; however, the agent was radioactive, emitting alpha irradiation that was concentrated in the reticuloendothelial system. Thorium has a biologic half-life of 400 years; within approximately 20 years, it became clear that patients who had been exposed to this agent had about a 100-fold increased incidence of hepatic and splenic tumors and a 20-fold rise in the incidence of leukemia. At the time of Thorotrast's introduction, the only known radiation effects were seen in those with very high occupational exposures, such as the original radiation physicist Madame Curie and the infamous radium dial painters who painted the watch dials of timepieces with radium and then dipped the brushes in their mouths.

It is my belief that the experience of the radiology community with Thorotrast parallels what is happening with CT scanning; the radiation risks associated with CT scanning are real and should serve as a wake-up call to all of us who read CT studies and order CT studies.

Putting Patients First

What can we as radiologists do to counsel our patients regarding the risk of radiation exposure from CT scans?

  1. Be aware of these issues when ordering CT studies, particularly in young patients or in patients with chronic conditions, such as Crohn's disease.

  2. Try to assess the real risk-benefit ratio from the study. Example: Will the renal stone CT study resulting in high radiation exposure really change the clinical management pathway in the setting of acute renal colic, especially in a young patient who may have multiple episodes over a lifetime and has a known history of renal and ureteral stones?

  3. Try to obtain imaging histories from old charts and from patients.

  4. Discuss cases with the radiologists when confronting these issues.

  5. The Radiation Safety Officer (RSO) is informed of all radiation issues that may arise in the hospital. Currently, we have an immediate notification of the RSO for greater than 30-minute fluoroscopy times in cardiac catheterization/angiography laboratories. These patients, even the elderly, may be subject to skin burns and other local effects from concentrated local fluoroscopic exposure and may need to be evaluated in 24-72 hours post procedure in cases of excessive exposure. This issue is a real one, and we have seen this in our practice.

  6. The RSO is also informed of excessive CT exposure. We have set an arbitrary threshold of 5 abdominal/pelvic CTs in a 2-year period in anyone under the age of 35. We are also monitoring on a case-by-case basis those patients who may have had excessive exposure via CT pulmonary arteriograms, head CTs in childhood/infancy, and neck CT studies. The CT technologists or radiologists bring these cases to the RSO's attention. The RSO will then review the case, the imaging, and clinical indications and decide whether a letter to the ordering clinician(s) is appropriate. Further management on a case-by-case basis may become necessary if continued exposure is ongoing.

Steven Birnbaum, MD
Radiation Safety Officer
Parkland Medical Center
Southern New Hampshire Medical Center

If you have comments or questions in regard to Dr. Birnbaum's efforts at safeguarding his colleagues and patients or Dr. Semelka's CT radiation piece, or you just want to share your own experience with CT scanning, please contact me at: rchevrier@medscape.net .

Robert Chevrier
Editorial Director
Medscape Radiology

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