Effect of arm position, presence of medical devices, and off-centering during acquisition of scout image on automatic tube voltage selection and current modulation in pediatric chest CT.

Young Jin Ryu,Ji Eun Park,Jung-Eun Cheon,Woo Sun Kim,Young Hun Choi,In-One Kim,Sebastian Tschauner

doi:10.1371/journal.pone.0195807

Abstract

PurposeTo evaluate the patients’ morphologic factors affecting radiation dose in pediatric chest CT.Materials and methodsFrom November 2013 to May 2015, 315 pediatric chest CT scans were obtained using a CT scanner, and classified into 5 groups according to the patients’ age. For each age group, the chest CT scans were divided into two subgroups. A cut-off value used was the 75th percentile of size-specific dose estimates (SSDE), age-specific diagnostic reference level (DRL): less than the 75th percentile of SSDE (Group A, n = 238) and greater than the 75th percentile of SSDE (Group B, n = 77). All CT scans were performed with the same protocol using automatic tube voltage selection and current modulation techniques. The morphologic factors of the patients including body mass index (BMI), arm angles, presence of medical devices in the scan field, and degree of off-centering within the CT gantry were compared between groups A and B.ResultsGroup B showed narrower arm angles on scout and coronal reformatted images, higher frequency of the presence of devices and higher BMI than group A (P < 0.001, P < 0.001; P = 0.018, and P < 0.001, respectively). In multivariate analysis, narrower arm angles, the presence of devices on the scout images and higher BMI were independently associated with higher SSDE (P = 0.001, P = 0.037, and P < 0.001, respectively).ConclusionsDuring acquisition of the scout images, arms-down position and the presence of medical devices were associated with a high radiation dose above age-specific DRLs in pediatric chest CT, regardless of repositioning before the actual scanning. In addition, off-centering had no clinical impact on radiation dose in the routine practice.

Highlights

Radiation exposure in children has become a great concern as CT images hold an important position in diagnostic algorithm and monitoring of therapeutic responses [1,2,3]
Narrower arm angles, the presence of devices on the scout images and higher body mass index (BMI) were independently associated with higher size-specific dose estimates (SSDE) (P = 0.001, P = 0.037, and P < 0.001, respectively)
During acquisition of the scout images, arms-down position and the presence of medical devices were associated with a high radiation dose above age-specific diagnostic reference level (DRL) in pediatric chest CT, regardless of repositioning before the actual scanning

Summary

Introduction

Radiation exposure in children has become a great concern as CT images hold an important position in diagnostic algorithm and monitoring of therapeutic responses [1,2,3]. A method combining an automatic tube voltage selection (ATVS) technique and automatic tube current modulation (ATCM) technique was introduced to reduce radiation dose while maintaining image quality [8,9,10,11]. With this method, the optimal tube voltage is automatically selected for each patient, and the tube current is modulated in real-time manner. Even though the level of tube voltage and tube current are largely determined by the body size and morphology in these techniques, several ancillary factors, such as presence of devices, patient off-centering, or arm positioning, have been reported to be important for tube current modulation and voltage selection in previous studies [12,13,14,15,16,17]

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