Patient dose increase caused by posteroanterior CT localizer radiographs.

INTRODUCTION

The aim of this study was to compare the output dose (volume CT dose index [ CTDI], and dose length product [DLP]) of automatic tube current modulation (ATCM) determined by localizer radiographs obtained in the anteroposterior (AP) and posteroanterior (PA) directions.

METHODS

One hundred and twenty-four patients who underwent upper abdomen and/or chest-to-pelvis computed tomography (CT) were included. Patients underwent two series of CT examinations, and localizer radiographs were obtained in the AP and PA directions. The horizontal diameter of the localizer radiograph, scan length, CTDI, and DLP were measured.

RESULTS

There was no significant difference in the scan length; however, all the other values were significantly higher in the PA direction. The mean horizontal diameter was 33.1 ± 2.6 cm and 35.4 ± 2.9 cm in the AP and PA directions of the localizer radiographs, respectively. The CTDI and DLP in the PA direction increased by approximately 7-8%. Bland-Altman plots between AP and PA localizer directions in upper abdominal CT showed a positive bias of 1.1 mGy and 30.0 mGy cm for CTDI and DLP, respectively. Correspondingly, chest-to-pelvic CT showed a positive bias of 0.93 mGy and 69.3 mGy cm for CTDI and DLP, respectively.

CONCLUSION

The output dose of ATCM determined by localizer radiographs obtained in the PA direction was increased compared to the AP direction. Localizer radiographs obtained in the AP direction should be preferred for optimizing the output dose using ATCM.

IMPLICATIONS FOR PRACTICE

Based on the evidence of this study, localizer radiographs obtained in the AP direction should be preferred for optimizing the output dose in CT examinations.