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An Automated Technique to Determine Patient Size for Obtaining Size Specific Dose Estimates From System Reported CT Dose Index

J Dave

J Dave¹*, V Zohrabian¹, E Gingold¹, (1) Thomas Jefferson University Hospital, Philadelphia, PA

SU-E-I-55 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:Size-Specific Dose Estimate (SSDE) uses patient size to produce an estimate of the radiation dose to the patient resulting from a CT scan. The purpose of this work was to develop an automated technique to determine patient size based on localizer radiograph and the center slice of the scanned volume for SSDE calculations.

Methods:This retrospective study was approved by the Institutional Review Board. Abdominal CT studies of 38 patients (age range:12-86 years) were evaluated. An automated software algorithm was developed in Matlab (The Mathworks Inc.). Using information from the dose report images, series that resulted in radiation dose to the patient and the central slice of each series were identified. The lateral dimensions for the patient size were obtained from the localizer radiograph and the central transaxial slice by calculating the FWHM of the Gaussian function fit using a linear least squares estimation to the central row profile in each image. Similarly the anterior posterior (AP) patient dimensions were calculated from the central column profile of the central transaxial slice. These dimensions were compared with manual measurements performed by a radiology resident blinded to the algorithm results.

Results:A significant difference was observed between manual size measurements (range:27.1-49.9cm) and automated measurements (range:24.2-45.5cm) techniques (p<0.001, mean difference: 6.0cm, 95% CI: 4.7 to 7.3cm) for lateral measurements from the localizer radiograph. For measurements from the center transaxial slice images, the mean difference between the manual (range:16.6- 42.4cm) and automated techniques (range:16.4-42.5cm) was 1cm (95% CI: 0.4 to 1.7cm; p<0.001) for the lateral dimension and was 0cm (95% CI: -0.4 to 0.4cm; p>0.821) for the AP dimension.

Conclusion:This automated algorithm may be used to obtain patient dimensions from CT images for calculation of the size specific dose estimate, and may eliminate the need to perform these measurements manually.

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