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In light of increasing frequency of CT examinations in the past decades, the aims of this prospective study were to investigate scatter radiation breast exposure in head CT and its dependence upon body constitution, and to assess the efficacy of lead shielding as a means of breast dose reduction. In 49 women referred to head CT for objective medical reasons one breast was covered with lead apron during CT scanning. Radiation doses were measured by use of thermoluminescent dosimeters, at skin of both breasts and over the apron. The doses were then compared as well as correlated to body mass index and meatus acusticus externus-to-dosimeter distance, respectively. Average exposure at the skin of the unshielded breast was 0.28 mGy (range 0.15-0.41 mGy), compared with 0.13 mGy (range 0.05-0.29 mGy) at the shielded breast. The doses showed a mean reduction by 57% due to lead shielding. At least half of breast exposure was imparted to the breast from outside, whereas the remainder results from internal scatter. The higher the body mass index, the higher the percentage of internal scatter in total breast dose. Although the level of scatter radiation to the breast is generally low during head CT examination, the use of lead cover enables recognizable further reduction of the exposure, and is recommended as a feasible and effective procedure of breast protection during CT of the head.