The dramatic increase of diagnostic imaging capabilities over the past decade has contributed to increased radiation
exposure to patient populations. Several factors have contributed to the increase in imaging procedures: wider
availability of imaging modalities, increase in technical capabilities, rise in demand by patients and clinicians,
favorable reimbursement, and lack of guidelines to control utilization. The primary focus of this research is to
provide in depth information about radiation doses that patients receive as a result of CT exams, with the initial
investigation involving abdominal CT exams. Current dose measurement methods (i.e. CTDIvol Computed
Tomography Dose Index) do not provide direct information about a patient's organ dose. We have developed a
method to determine CTDIvol normalized organ doses using a set of organ specific exponential regression
equations. These exponential equations along with measured CTDIvol are used to calculate organ dose estimates
from abdominal CT scans for eight different patient models. For each patient, organ dose and CTDIvol were
estimated for an abdominal CT scan. We then modified the DICOM Radiation Dose Structured Report (RDSR) to
store the pertinent patient information on radiation dose to their abdominal organs.
The purpose of this study was to investigate the accuracy of Monte Carlo simulated organ doses using cylindrical ROIs
within the organs of patient models as an alternative method to full organ segmentations. Full segmentation and
placement of circular ROIs at the approximate volumetric centroid of liver, kidneys and spleen were performed for 20
patient models. For liver and spleen, ROIs with 2cm diameter were placed on 5 consecutive slices; for the kidneys 1cm
ROIs were used. Voxelized models were generated and both fixed and modulated tube current simulations were
performed and organ doses for each method (full segmentation and ROIs) were recorded. For the fixed tube current
simulations, doses simulated using circular ROIs differed from those simulated using full segmentations: for liver, these
differences ranged from -5.6% to 10.8% with a Root Mean Square (RMS) difference of 5.9%. For spleen these
differences ranged from -9.5% to 5.7% with an RMS of 5.17%; and for kidney the differences ranged from -12.9% to
14.4% for left kidney with an RMS of 6.8%, and from -12.3% to 12.8% for right kidney with an RMS of 6.6%. Full
body segmentations need expertise and are time consuming. Instead using circular ROIs to approximate the full
segmentation would simplify this task and make dose calculations for a larger set of models feasible. It was shown that
dose calculations using ROIs are comparable to those using full segmentations. For the fixed current simulations the
maximum RMS value was 6.8% and for the TCM it was 6.9%.
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