Characteristics of extrafocal radiation and its potential significance in pediatric radiology.

Extrafocal radiation was investigated using four different rotating-anode radiographic units currently employed in a pediatric hospital. It was found to exhibit significant penetration, with an effective energy only slightly lower than that of the primary radiation. The percentage of extrafocal relative to focal radiation in pediatric procedures involving rare-earth screens ranged from 2 to 15%. The ratio of extrafocal to focal radiation tended to increase with increasing kVp, mA, and field size but was independent of focal spot size. Since extrafocal radiation may extend significantly outside of the primary collimated field, radiosensitive organs such as the gonads, thyroid, and eyes which are assumed to be shielded may actually receive as much as 25 mR per radiograph.