For patients, computerized tomography (CT) scans are simple and painless. The machine looks like a big doughnut standing on its side. The patient lies on a slab that slides through the doughnut’s hole until the part of the body to be scanned is positioned beneath a rotating ring that contains an X-ray camera. Each rotation scans a “slice” of the body part. The patient feels nothing. As the camera rotates around the patient, the bed slides through the doughnut taking pictures. The procedure takes less than 10 minutes and generates data that a computer combines into a portrait of the area scanned, yielding images far superior to a shadowy two-dimensional X-ray.

CT scans have saved countless lives by allowing doctors to detect injuries and diseases that don’t show up on standard X-rays. The scans also have prevented misdiagnoses and unnecessary surgeries. It’s not surprising that their use by doctors has surged over the last two decades.

Yet this diagnostic power carries a cost: Each of the rotations exposes patients to doses of radiation that accumulate. Each CT scan exposes patients to between 100 and 500 times the amount of radiation in an X-ray. “The same doses that people got from the Hiroshima bomb drop, which we now know increases the risk of cancer development,” said Rob Goodman, MB BChir, interim chair and professor of diagnostic radiology and chief of pediatric imaging.

When Goodman came to Yale from Oxford in 2003, he was alarmed by the excessive use of CT scans here. Americans were getting three times more medical radiation than were Europeans. Goodman was especially worried about the effects on children, because their smaller, rapidly changing bodies are more susceptible to ionizing radiation and hence to the risk of cancer from it.

Goodman began a campaign to shrink the radiation exposure of children who came to Yale-New Haven Hospital (YNHH). He conducted grand rounds for pediatricians on reducing radiation doses and urged them to consider such alternatives to CT scans as ultrasound. He also worked with the hospital’s medical physicists to tweak the CT scanners to give children the lowest possible dose while still making images acceptable for diagnosis.

Goodman’s efforts coincided with a growing national awareness about the risks of medical imaging, particularly for children. In January 2008 the Alliance for Radiation Safety in Pediatric Imaging, representing more than 70 medical organizations, launched the Image Gently campaign to educate doctors and the public about cumulative radiation exposure. Manufacturers began building scanners that automatically adjusted the dose based on the patient’s age and weight, as well as the sensitivity of the area to be scanned.

These steps have raised consciousness and lowered CT use, but children are still getting too much radiation. In June, a study published in JAMA Pediatrics reported that of the estimated 4 million CT scans given every year to children in the United States under age 15, a third are unnecessary and may lead to 5,000 cases of cancer. In the same month, a study published in The Lancet found that children who get multiple CT scans have a slightly higher risk of developing leukemia or brain cancer.

At YNHH, Goodman’s efforts have paid off. In data compiled by the American College of Radiology’s Dose Index Registry, which tracks and categorizes the radiation given by CT scanners in U.S. hospitals, YNHH recorded the lowest doses of any hospital in the country in many age groups and types of pediatric CT studies.

The hospital’s own statistics tell a similar story. In 2003 YNHH had three CT scanners and did 4,844 CT scans on children. In 2012, despite now having seven scanners, the hospital did only 2,344 studies on children. Those numbers took even Goodman by surprise.

Goodman expects the numbers to drop further as MRI, which emits no radiation, replaces CT scans for many diagnoses. His campaign to lower radiation doses at YNHH has been so successful that he now sometimes finds himself urging clinicians and parents not to avoid CT scans in the correct clinical setting. “If the suspicion is high that your child may have a significant lesion in the lung,” he said, “be reassured that the CT radiation doses at Yale are the lowest in the country and doing the scan is what’s best for the patient.”