Size-Specific Dose Estimates for Thoracic Imaging in 320 Row Detector Computed Tomography

Abstract

The patient dose from CT scan is normally displayed in Dose Length Product (DLP) and volume CT dose index (CTDIvol). Actually, CTDIvol represents the scanner output, does not address patient size, can be used to estimate patient radiation dose but the dose value is inaccurate as it is estimated from the cylindrical phantom of particular size. AAPM Report no.204 [1] introduced in 2011 and AAPM Report no.220 [2] introduced in 2014 on the size-specific dose estimates (SSDEs) for CT examination in order to provide high accuracy on radiation dose to the patient. The purpose of this study was to determine the patient radiation dose using SSDEs for thoracic imaging in 320 MDCT and the parameters influenced SSDEs. This study is retrospective analysis with 230 patients, 115 male and 115 female of the age range from 18 to 93 years old, the selected weight range from 40 to 70 kg. All of the patients underwent the thoracic contrast enhancement with venous phase protocol scanned by 320 MDCT. The patient radiation dose in terms of SSDE was calculated based on AP+LAT dimension, effective diameter, and water equivalent diameter. The conversion factors following the body size and composition according to the AAPM no.204 and 220 recommendations were applied. SSDE was measured from middle slice of chest and middle slice of scan range. The results showed that the SSDE calculated from the middle of scan range was a little higher than SSDE calculated from middle of organ. At the middle slice of organ, the range of SSDEAP+LAT SSDEEFF and SSDEDw were 10.50-24.45, 10.43-24.25 and 11.66-26.83 mGy respectively. At the middle slice of scan range, the range of SSDEAP+LAT, SSDEEFF and SSDEDw were 10.83-24.85, 10.70-24.70 and 11.33-27.13 mGy respectively. The correlation of CTDIvol, body weight, BMI, AP+LAT dimension, effective diameter and water equivalent diameter with SSDE were moderately linear relationship. In conclusions, SSDE had been estimated using 3 methods (SSDEAP+LAT, SSDEEFF and SSDEDw) of body configurations in CT dosimetry. SSDEDw is most appropriate for determination as the CT patient dose indicator further from CTDIvol especially in various body sizes and body composition in thorax region.