FDA Proposal Aims at Lower Doses for Pediatric X-Ray

James Brice

May 18, 2012

May 18, 2012 — The realization that 1-size-fits-all radiography can be bad for children has forged a coalition between federal regulators, physicians, physicists, and medical device manufacturers to make medical imaging involving exposure to ionizing radiation safer for young patients.

The US Food and Drug Administration (FDA) took action May 9 as part of this collaboration by releasing proposed guidance encouraging manufacturers to consider the safety of children in the design of new X-ray imaging devices. The federal agency recommended equipment features that would alter the performance of X-ray imaging devices designed for general clinical use to address the specific requirements of younger patients.

The guidance was published after more than a decade of explosive use growth linked to medical applications of multislice computed tomography (CT), positron emission tomography, fluoroscopically guided biopsies, and other minimally invasive image-guided interventional procedures. All these events expose patients to ionizing radiation.

Their immediate benefits are thought to usually outweigh their risks, but radiation is known to carry a hard-to-calculate elevated long-term probability of induced cancers, said Marta Hernanz-Schulman, MD, chair of the American College of Radiology Pediatric Imaging Commission.

Childhood Vulnerability

Children are especially vulnerable because they absorb more radiation per volume of tissue than adults. They are also growing, which means they have relatively more cell divisions, making them more radio-sensitive than adults. In addition, a longer life awaits most children than adults, presenting them with more time for radiation-induced cancers to develop, Dr. Hernanz-Schulman told Medscape Medical News.

Beginning in February 2010, the FDA has been working with the Alliance for Radiation Safety in Pediatric Imaging (ARSPI) and the Medical Imaging and Technology Alliance (MITA) to reduce pediatric exposure to ionizing radiation from medical imaging. Their combined efforts also involve educational mechanisms to inform the public and physicians about appropriate applications of CT and other X-ray-based imaging technologies.

ARSPI is a coalition of 29 organizations. It launched its Image Gently campaign in January 2008 to raise awareness of opportunities to reduce radiation dose estimates used in pediatric imaging.

MITA is a public interest group representing the interests of 66 medical imaging equipment manufacturers. It supports initiatives in line with minimizing pediatric dose, including equipment performance features that reduce exposure, instrumentation that alerts users during CT procedures when recommended doses have been exceeded, and information technologies that track cumulative radiation doses for individual patients.

The guidance encourages manufacturers to design new X-ray and CT systems with the needs of children in mind, Thalia Mills, PhD, a medical physicist from the FDA's Center for Devices and Radiological Health told Medscape Medical News.

This concept is based, in part, on the knowledge that children imaged at pediatric hospitals are generally exposed to less ionizing radiation during X-ray and CT procedures than children examined at general community hospitals, Jana Delfino, PhD, a biomedical engineer also from the FDA's Center for Devices and Radiological Health, told Medscape Medical News.

The guidance is designed to build some of the staff intelligence responsible for the lower dosage at specialized children's hospitals into the next generation of imaging machines, so children receive optimal doses everywhere are imaged, she said.

"We hope this guidance makes the job of the [radiological] technologist easier because new equipment will arrive at the hospital with child-size protocols built in, along with instructions to ensure that they used," she said.

Warning Labels for Noncompliant Equipment

The proposal would ask manufacturers seeking 510(k) clearance for new products to submit data supporting the safety and effectiveness of the new device for children. Vendors that do not provide information assuring the FDA of the safety and effectiveness of X-ray devices for children on a voluntary basis would be required to display a label on the device indicating the equipment is not appropriate for patients under a given weight and size, Dr. Mills said.

Applicable imaging systems include those for conventional X-ray-based radiography, X-ray angiography, fluoroscopy, and medical and dental CT.

X-ray imaging device with indications for pediatric imaging should include features geared toward imaging smaller patients. Example features include:

  • specific preset pediatric control settings;

  • pediatric procedures, labeling, and protocols minimizing radiation exposure;

  • display and recording of patient dose or dose index and the ability to record patient information such as age, height, and weight;

  • interactive software display features that alert the user to special pediatric issue relevant to machine settings for acquiring images;

  • automatic exposure controls calibrated for pediatric patients;

  • a user guide dedicated to pediatric use;

  • preconfigured default pediatric protocols;

  • phantoms representing 1-month, 5-year-old, 12-year-old, and adult patients sizes enabling users to account for child and adult body types during routine assessments of imaging quality and dose;

  • educational material covering aspects of the equipment relevant to pediatric imaging, including dose-reducing features and protocols customized for children; and

  • user training covering built-in features providing dose reduction and image quality improvement, with attention to dose-savings features for children.

The educational recommendations are especially important to ensure that research and development investments into reducing dose are not wasted on end users who do not know how to apply it, said Dr. Hernanz-Schulman. The guidance recommends continuous opportunities for education to account for job turnover and new entrants who may not be expert in a scanner's operation.

The proposed guidance reflects FDA outreach to pediatric radiologists, physicists, and technologists for ideas that promise to reduce pediatric exposure, she said.

"The FDA is basically channeling all our voices and giving it to the manufacturers in a systematic way that makes sense to them," she added. "The manufacturers want to know how they can do this. They will be very keen on following through," said Dr. Hernanz Schulman.

The FDA has planned a workshop in Silver Spring, Maryland, on July 15 to receive public comments. The 120-day public comment period ends September 7, 2012.

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