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The findings argue for the judicious use of computed tomography ( CT ) scanning and a risk/benefit analysis to limit radiation exposure.

Low-dose radiation used to evaluate trauma patients can increase lifetime risk for cancer, with greater risk for younger patients and for girls. The findings, presented at the American College of Surgeons 96th Annual Clinical Congress, argue for the judicious use of computed tomography ( CT ) scanning and a risk/benefit analysis to limit radiation exposure.

Senior author Margaret Griffen, MD, trauma surgeon at Inova Fairfax Hospital and Regional Trauma Center in Falls Church, Virginia, said medical radiation accounts for about 11% of all radiation exposure in the American population, and includes medical x-rays, nuclear medicine scans, and CT scans. In 2005, 62 million CT scans were performed, 4 million of which were on children.

Dr. Griffen and coworkers undertook a prospective study to examine the actual radiation dosage to a trauma patient during routine evaluation and treatment. Comparing these figures with data on cancer risk, they were able to determine the possible cancer risk and cancer mortality at the organ level.

The study comprised all trauma-team-activated patients being evaluated with CT scans at a level 1 trauma center between September 2009 and January 2010. Four dosimeters were placed along a Plexiglas strip at 4 surrogate reference points, corresponding to the level of head, neck, chest, and gonads. Strips were placed behind a patient at the midclavicle and midinguinal ligament line. Each strip had a patient identifier on it and was used each time a patient received a scan. The strips were collected at discharge.

All the strips were read by a single observer, who calculated a whole body dose. To get organ-specific doses, the researchers constructed 3 phantom models — an infant, a child, and an adult size. Dosimetry strips were placed behind the phantoms and within the bodies at specific organ locations. "From this, we could then create a cross-reference coefficient that we could use to multiply by the dosimeter readings for our specific patients and come up with organ-specific radiation dosing in milligrays," Dr. Griffen said.

The study involved 462 patients, the majority of them male (63%) and adults (most younger than 50 years), and almost all with blunt trauma (92%). They received an average of 3.5 CT scans. The average Injury Severity Score was 7.9, and the majority (46%) of patients were discharged home.

Dr. Griffen reported that total body radiation exposure increased with increasing patient age. "The average exposure total for males was about 61 mGy. The average exposure for females was about 58 or 59 mGy," she said. The average exposure for patients who went home from the emergency department was 58 mGy for males and 42 mGy for females. Organ-specific doses were higher for the head and thyroid and lower for the chest and gonads for both males and females, with the females getting somewhat less radiation.

Using the 2006 Biological Effects of Ionizing Radiation model (BEIR VII, phase 2), put out by the National Academies, which assumes a linear no-threshold relationship in which every dose counts and in which dose is proportional to risk, the researchers estimated organ-specific risks using their own data and the BEIR tables.

For thyroid cancer, males had much lower risk, about 10 to 12 per 100,000, when exposed at a very young age, whereas females had a potential lifetime risk for thyroid cancer of about 120 per 100,000. Risk for thyroid cancer diminished sharply if exposure occurred in the second decade of life for females, and reached an age-equivalent level in males only with exposures in the fifth decade.

Similarly, for female breast cancer, exposure at a very young age (first decade) greatly increased the lifetime risk, at about 100 per 100,000. For breast cancer mortality, "at a very young age, exposing these patients to radiation increases their likelihood of cancer mortality," Dr. Griffen said. Uterine and ovarian cancer rates were low and fairly constant, regardless of age at exposures.

She concluded that low-dose ionizing radiation for the evaluation of trauma patients potentially puts them at greater risk for cancer and cancer mortality. "The judicious use of [the] CT scan has to be part of our practice," she advised. "Age at exposure and gender do play a role in their future risk." She said future plans include looking at the 46% of patients who are sent home from the emergency department to see if the researchers can make an impact there.

Session comoderator Thomas Scalea, MD, professor of surgery and director of the program in trauma at the University of Maryland School of Medicine in Baltimore, said that the use of CT scanning helped Dr. Griffen's trauma unit send almost half the patients home rather than hospitalizing and observing them. "The alternative would be to go on to a clinical exam, which we know means you will miss some injuries. So how many injuries are you willing to miss in order to avoid irradiating these people?" he asked.

Dr. Griffen agreed that that was the critical question, giving as an example the potentially catastrophic nature of missing even 1 cervical spine injury. She suggested that there might be ways to observe some patients without admitting them to the hospital to adequately evaluate them without doing a CT scan.

Comoderator Ronald Maier, MD, professor and vice chair of surgery at the University of Washington and director of the Northwest Regional Trauma Center in Seattle, asked if the results of the prediction model (which he noted is not experimental proof) are sufficiently worrisome that magnetic resonance imaging ( MRI ) rather than CT scanning should be used. Dr. Griffen replied that MRI would probably not be feasible because it is too slow and not useful enough to replace CT scanning in the trauma setting.

Source: ACS

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