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Do Weight-Based Pediatric CT Abdomen Protocols Provide Similar Size-Specific Dose Estimates for Similar Patient Effective Diameters?


M Supanich

MP Supanich1*, (1) Henry Ford Hospital, Detroit, MI

WE-A-218-5 Wednesday 8:00:00 AM - 9:55:00 AM Room: 218

Purpose:
The use of weight-based acquisition techniques for CT examinations of pediatric patients is a common practice in the imaging community. AAPM Report 204 reported on conversion factors for Size Specific Dose Estimates (SSDE) based on patient effective diameter. This study examines the relationship between the use of weight-based Pediatric CT abdominal acquisitions at one institution and the resultant SSDE.

Methods:
A total of 36 Pediatric Abdomen and Pelvis CTs acquired on scanners from 2 different manufacturers at 120 kVp and using fixed tube current based on reported patient weight were analyzed. The fixed tube currents at each weight range were chosen to match CTDIvol (32 cm phantom) across scanners.
Effective diameter was established by thresholding the mid-scan range image to determine patient area and was calculated using eXposureTM from Radimetrics. The area is then converted to a circle of equivalent diameter.

SSDE was determined using the effective diameter for each study and the recorded CTDIvol. The eXposureTM software utilized AAPM Report 204 look-up-tables (LUTs) of conversion factors and interpolation to determine the correct normalization factor for each study which is then used to scale the CTDIvol to the final SSDE value.

Results:
Weak correlation was observed between effective diameter and SSDE, with SSDE values varying by as much as a factor of 2 for effective diameters within 0.5 cm. A slight decrease in average SSDE was observed at larger effective diameters.

Conclusion:
The weight-based acquisition protocols analyzed in this study do not effectively match patient effective diameter and radiation dose. Technique parameters based on patient effective diameter should provide better dose equivalence for patients of equal cross-sectional area. Assessment of image quality and the evaluation of acquisition protocols based on diameter will be pursued in the future.


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