Simplifying size-specific radiation dose estimates in pediatric CT.

OBJECTIVE Size-specific dose estimates (SSDEs) require manual measurement of torso diameters for individual patients--anteroposterior (hereafter, D(AP)), lateral (hereafter, D(LAT)), and effective (hereafter, D(E))--which can be tedious in clinical settings. We aimed to determine whether body weight can be used as a surrogate for measuring diameter in children. MATERIALS AND METHODS D(AP) and D(LAT) were measured in 522 consecutive CT examinations (chest, 187 and abdomen-pelvis, 335) performed in 483 (± SD) children (13 ± 7 years). Effective diameter (D(E1)) was calculated as the square root of the product of D(AP) and D(LAT). A second measurement of effective diameter (D(E2)) was obtained using automated software. Correlation coefficients between patient body weight, age, and diameter were measured in addition to 95% prediction interval analysis for diameters corresponding to body weight. RESULTS Median body weight was 51 kg, and mean D(AP), D(LAT), D(E1), and D(E2) were 207.1 ± 50.8 mm, 289.8 ± 72.6 mm, 243.3 ± 62.0 mm, and 233.6 ± 55.4 mm, respectively. Overall body weight had a strong correlation with diameter (0.88, 0.85, 0.86, and 0.93 respectively; all p < 0.0001). SSDE measured using body weight was statistically not different than SSDE measured using effective diameters (p = 0.9). Children weighing less than 27 kg and between 46 and 100 kg had statistically significant correlations with torso diameters, whereas only anteroposterior and effective diameters were correlated with children weighing between 27 and 45 kg. Children less than 4 years old had strong correlation with all diameters. Adolescents (15-18 years) did not have statistically significant correlation with any of the diameters. CONCLUSION Body weight, instead of body diameter, can be used as a surrogate to estimate size-specific dose in children, making dose estimation clinically simpler and more rapid.