Program Information
Investigation of the Effective Dose From Bolus Tracking Acquisitions at Different Anatomical Locations in the Chest for CT
P Nowik*, R Bujila, D Merzan, Dept. of Medical Physics, Karolinska University Hospital, Stockholm, Sweden
Presentations
TU-G-CAMPUS-I-6 (Tuesday, July 14, 2015) 5:00 PM - 5:30 PM Room: Exhibit Hall
PURPOSE: Stationary table acquisitions (Bolus tracking) in X-ray Computed Tomography (CT) can result in dose length products (DLP) comparable to spiral scans. It is today unclear whether or not the effective dose (E) for Bolus Tracking can be approximated using target region specific conversion factors (E/DLP). The purpose of this study was to investigate how E depends on the anatomical location of the Bolus Tracking in relation to Chest CT scans with the same DLP.
METHODS: Effective doses were approximated for the ICRP 110 adult Reference Male (AM) and adult Reference Female (FM) computational voxel phantoms using software for CT dose approximations (pre-simulated MC data). The effective dose was first approximated for a Chest CT scan using spiral technique and a CTDIvol (32 cm) of 6 mGy. The effective dose from the spiral scan was then compared to E approximated for contiguous Bolus Tracking acquisitions (1 cm separation), with a total collimation of 1 cm, over different locations of the chest of the voxel phantoms. The number of rotations used for the Bolus Tracking acquisitions was adjusted to yield the same DLP (32 cm) as the spiral scan.
RESULTS: Depending on the anatomical location of the Bolus Tracking, E ranged by factors of 1.3 to 6.8 for the AM phantom and 1.4 to 3.3 for the AF phantom, compared to the effective dose of the spiral scans. The greatest E for the Bolus Tracking acquisitions was observed for anatomical locations coinciding with breast tissue. This can be expected as breast tissue has a high tissue weighting factor in the calculation of E.
CONCLUSION: For Chest CT scans, the effective dose from Bolus Tracking is highly dependent on the anatomical location where the scan is administered and will not always accurately be represented using target region specific conversion factors.
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