Difference between volume Computed Tomography Dose Index (CTDIvol) and Size Specific Dose Estimates (SSDE) in abdomen- and thorax protocols in patients of different sizes in different CT scanners.

Abstract

Background: Volume Computed Tomography Dose Index (CTDIvol) only provides information about the radiation dose delivered by a CT scanner. The Size Specific Dose Estimate (SSDE) introduced by the American Association of Physicists in Medicine (AAPM) takes into account patient size and gives a more accurate representation of received radiation doses. The aim of the study is to examine the difference between CTDIvol and estimated SSDE values in thoracic and abdominal scans in different CT scanners and investigate the level of under- or overestimation of doses in patients of various sizes. Methods: Retrospective data collection included 500 thoracic scans and 500 abdominal scans from four different scanners from two separate vendors. Age, CTDIvol, AP- and LAT- diameter were gathered from the Picture Archiving and Communication System (PACS), effective diameter (Deff), and water equivalent diameter (Dw) were calculated in Excel. A t-test was used to determine if there was a statistically significant difference between CTDIvol and estimated SSDE. Results: In all scanners, there was a statistically significant difference between CTDIvol and estimated SSDE values (p <0.05). In abdominal scans, the under- or overestimation of doses ranged from 41% in patients with a Deff of 18-21.9 cm to -14% in patients with a Deff of 38-41.9 cm. In the thoracic scans, the underestimation of doses ranged from 43% in patients with a Dw of 18.-21.9 cm to 6% in patients with a Dw of 34-37.9 cm. Conclusion: By taking into account the patient size and the scanner output, we found that CTDIvol underestimates radiation doses to patients of small sizes (<32 cm) and overestimates doses to some, but not all, larger patients (>32 cm).