AJR: Weight protocol can lower rad dose with pediatric CT

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By making changes in routine pediatric chest CT protocol regarding the patient’s weight, significant radiation dose reduction can be achieved within this patient population, according to a study published in the May edition of the American Journal of Roentgenology.

Jee-Eun Kim, MD, from the department of radiology at Lucile Packard Children’s Hospital, Stanford University School of Medicine, in Stanford, Calif., and colleagues designed their study to quantify the effect of changes made to the CT chest protocol on patient dose, image quality, and image noise when using a kilovoltage (kVp)-lowering strategy.

“CT exams are commonly performed in the pediatric population,” said Beverley Newman, MD, co-author of the study. “However radiation dose related to CT has become a public health concern, and appropriate reduction of radiation dose has become an important goal in pediatric CT.”

The researchers retrospectively selected 120 children (60 in 2006 and 60 in 2008) who underwent chest CT. In each group there were 30 children weighing less than 15 kg and 30 between 15 and 60 kg. In 2006 the CT protocol was 120 kVp and in 2008, the kVp was 80 for less than 15 kg and 100 for 15–60 kg, explained the authors. For each exam, the volume CT dose index and dose-length product were recorded. Effective dose was estimated and image noise was measured. Overall image quality was subjectively evaluated, they wrote.

According to Kim and colleagues, in pediatric patients with a weight less than 15 kg, the volume CT dose index was reduced by 73 percent, the dose-length product, by 75 percent and the effective dose was cut by 73 percent.  For the patients with a weight range of 15-60 kg, volume CT dose index, dose-length product and the effective dose were reduced by 45, 44 and 48 percent, respectively.

In addition, measured noise was found to increase by 55 percent in the patients that weighed less than 15 kg and 41 percent in the 15-60 kg cohort. However, “Increased noise was considered an acceptable trade-off for decreased dose, and image quality was acceptable. No study was considered nondiagnostic,” wrote the researchers.

Referencing other studies, the authors said that the findings of their research agree that tube voltage reduction is particularly useful when patient body size is small. “This is because there is less intervening material to absorb the radiation in smaller phantoms,” they explained.

“Significant dose reduction can be achieved for routine pediatric chest CT by paying attention to simple protocol adjustments based upon patient weight. This is especially important for the younger, most radiation sensitive children," concluded Kim and colleagues.