Volume computed tomography dose index (CTDIvol) and size-specific dose estimate (SSDE) for tube current modulation (TCM) in CT scanning

In the tube current modulation (TCM) technique, tube current is changed dynamically during the scanning process. To quantify the effect of a dynamic tube current, a distinct calculator is needed to estimate the CT output radiation dose in terms of volume CT dose index (CTDIvol) and individual patient dose in terms of size-specific dose estimate (SSDE). This study developed a specific calculator for CT scanning using the TCM technique. The tube current was extracted from the DICOM header for every slice, and averaged over the scan length. The water equivalent diameter (Dw) and SSDE values were calculated for each tube rotation. The software was retrospectively applied to 57 patients who had undergone abdominal and thoracic CT examinations using a multi-detector CT, the Somatom Emotion 6. The differences between the calculated CTDIvol and the CTDIvol reported by the CT scanner were 4.4 ± 1.2% and 6.0 ± 2.0% for abdominal and thoracic examinations, respectively. The average tube current was found to be linearly correlated with Dw with R2 values of 0.707 and 0.696 for abdominal and thoracic examinations, respectively. The average tube current was also linearly and strongly correlated with the SSDE with R2 values of 0.941 and 0.887 for abdominal and thoracic examinations, respectively. Calculator for estimating CTDIvol and SSDE specifically for TCM in CT scanning has been successfully developed. The difference between calculated CTDIvol values using this calculator and reported CTDIvol values were less than 10%.