Tailoring dose to body shape optimizes pediatric CT

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BOSTON--Manipulation of kVp (kilovoltage peak) and mAs (tube current flow) according to a patient's body shape may help reduce CT radiation dose in pediatric patients, according to a study presented today at the 2009 annual meeting of the American Roentgen Ray Society (ARRS).

The investigators said that ll measurements were taken using a 16-slice CT scanner (Siemens Healthcare). Center line dose was measured using a 100 mm pencil probe ion chamber with an electrometer (Victoreen Instruments) and standard CT dose index phantoms with diameters of 10, 16 and 32 cm.

Researchers from the Cleveland Clinic Children's Hospital used phantoms that were 10, 16 and 32 cm in diameter (canvases of the average waist sizes for children two to 18 years of age) during the study. They made 120 dose measurements using various kVp and mAs levels.

The lowest dose found on the 10 cm was 12 mGy; the lowest dose found on the 16 cm was 19 mGy; and the lowest dose found on the 32 cm was 20 mGy," said Janet Reid, MD, and William Davros, MD, lead authors of the study.

The researchers noted that there are absolute size limitations to dose reduction with kVp for an acceptable noise value such that increases in mAs at low kVp in larger patients would lead to unacceptably large dose levels without achieving an acceptable noise level.

The investigators said that their results showed that although dose reduction is easily achieved through manipulation of mAs, it may be preferable to reduce the dose by adjusting the kVp, especially in the setting of iodinated contrast-enhanced scans which takes advantage of the higher k-edge absorption (enhancing the shades of grey) at a lower kVp.

"Our hopes are to tailor a patient's radiation dose to their body shape, not just their weight and age," said Reid and Davros. "In doing so, a patient will get a decreased radiation dose that is tailored to them. A personalized radiation dose."