Estimated patient dose indexes in adult and pediatric mdct: Comparison of automatic tube voltage selection with fixed tube current, fixed tube voltage, and weight-based protocols

OBJECTIVE. The purposes of this study were to determine the differences in estimated volumetric CT dose index (CTDI_vol) obtained from the topogram before abdominal and pelvic MDCT in adult and pediatric patients using a scan type-based algorithm for selecting kilovoltage (CARE kV) and a fixed and a weight-based Quality Reference mAs for selecting tube (gmAs) current-exposure time product, in comparison with standard protocols, and to determine the bias and variability of estimated CTDI_vol vis-à-vis actual CTDI_vol using the standard protocols. MATERIALS AND METHODS. During a 14-month period, 312 adult and pediatric patients referred for abdominal and pelvic MDCT were included in the study. For all patients, the estimated CTDI_vol based on the topogram was recorded: protocol A, CARE kV on and 210 gmAs; protocol B, CARE kV on and 1 gmAs times patient weight (in pounds); and protocol C (standard protocol), CARE kV off, 120 kVp, and 1 gmAs times patient weight (in pounds). For the pediatric patients, estimated CTDI_vol for the standard protocol D was calculated with 120 kVp and 150 gmAs. All patients were scanned with the standard protocols, and the actual CTDI_vol was recorded. Linear regression models compared the CTDI_vol of the three protocols in adults and the fourth for children. The estimated and actual CTDI_vol were compared using a t test. RESULTS. Protocol B yielded the lowest estimated CTDI_vol (mean, 13.2 mGy for adults and 3.5 mGy for pediatric patients). The estimated CTDI_vol overestimated the actual CTDI_vol by, on average, 1.07 mGy for adults and 0.3 mGy for children. CONCLUSION. CARE kV appears to reduce estimated CTDI_vol vis-à-vis standard protocols only when a weight-based gmAs is used. Prescan estimated CTDI_vol calculations appear to generally overestimate actual CTDI_vol.