Fifty-eighth annual meeting of the american association of physicists in medicine
SU-F-I-48: Variability in CT Scanning Over-Range Across Clinical Operation
Inconsistency in the scan range for a given protocol can be a source of variability in patient dose. The purpose of this study was to determine the variability in the over-scan length in clinical CT operation for chest and abdominopelvic (A&P) protocols.
A total of 51 abdomen-pelvis and 121 chest CT exams were randomly selected from our clinical database. A commercial dose monitoring solution was used to extract and database the total exposure area and the geometrical information related to automatically-segmented anatomical landmarks for each target region. The data were exported off-line for the statistical analysis. The over-scan length (delta) was calculated as the difference between the real scanned length and ideal scanning length based on the anatomical landmarks for each target region.
The mean delta for abdomen-pelvis exams was 12 mm (median 8 mm; min −191 mm; max 158 mm; standard deviation 71 mm). The average delta values at the interfaces with the chest and lower extremity regions were 69 mm and −57 mm, respectively. For chest exams, the average delta was 91 mm (median 93 mm; min 36 mm; max 190 mm; standard deviation 29 mm), and the average delta values at interfaces with the neck and abdomen regions were 26 mm and 65 mm, respectively. The percentage delta mean related to the abdomen-pelvis and chest lengths were 3% and 45%, respectively.
Although there is greater over-scan in the chest region, there is considerably more variability in the over-scan area for abdomen-pelvis exams. Estimation of the over-scan length must be included in the effective dose estimates, which uses different coefficients for different target region (ICRP 102). Furthermore, knowledge of over-scan lengths and variability can guide steps to improve clinical consistency and operation.