Consider low dose CT in children with DDH to reduce radiation exposure

CHICAGO — Overall, the dosage of radiation that children with developmental dysplasia of the hip (DDH) are exposed to in the course of their treatment was higher than average for patients that have plain film radiographs and the long-term effect was unknown, according to research presented at the American Academy of Orthopaedic Surgeons Annual Meeting.

"Plain films were shown to contribute heavily to the overall radiation dose,” Chad A. Hills, DO, said in a presentation here. “In spite of a relatively low risk, it is certainly not zero, and long-term consequences are not known. Alternative imaging should be considered, especially in those patients with bilateral involvement or those who were exposed to multiple reductions with associated advanced imaging."

The "cumulative effect" of CT scans on patients with developmental dysplasia is also unknown, according to Hills.

To investigate this area, Hills and colleagues performed a retrospective chart review of all children with hip dysplasia treated between 2006 and 2011 and recorded their pelvic radiograph, CT scan and fluoroscopic time. They then used standard radiation dose conversions to sum up the total radiation exposure for the fluoroscopies and radiographs and used an on-line radiation estimator with patient age and the dose length product to estimate exposure from the CT scans. The 60 patients that Hills and his co-authors singled out from the charts had undergone reduction of dislocated hips and had postreduction CT scans.

The dose of radiation that was found was 6.89 mSv per CT scan.

During the last 2 years of the study, the team followed a low-dose protocol, which brought down the radiation level from the CT scans down to 2.89 mSv per CT scan, based on the results.

The average per patient dose of radiation was 4.20 mSv for plain films and 0.15 mSv for fluoroscopy and the total post-reduction radiation dose per patient was 11.24 mSv.

Sixty-one percent of that total exposure was attributed to the CT scans. The total radiation does during the 2-year period when the low-dose protocol was used was 7.19 mSv per patient, with 39% due to the CT scans.

"After a successful reduction, the CT scans are a ‘one and done’ event,” but physicians continue to take plain films of these patients into adulthood to ensure they develop normally, Hills said.

The total projected dose of radiation when following the patients on plain film into adulthood, every 2 years as is typical, was 10.46 mSv per patient, Hills said, noting the average dose of radiation a person gets per year in the United States is 3 mSv.

"The relationship between radiation exposure and the development of cancer has been shown and everything that can be done to limit this radiation should be performed,” Hills said.

Reference:

Hills CA. Paper #80. Presented at: American Academy of Orthopaedic Surgeons Annual Meeting; March 19-23, 2013; Chicago.

Disclosure: Hills has no relevant financial disclosures.