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TU-H-CAMPUS-IeP1-05: A Framework for the Analytic Calculation of Patient-Specific Dose Distribution Due to CBCT Scan for IGRT.

PURPOSE
To investigate the feasibility of an analytic framework to estimate patients' absorbed dose distribution owing to daily cone-beam CT scan for image-guided radiation treatment.


METHODS
To compute total absorbed dose distribution, we separated the framework into primary and scattered dose calculations. Using the source parameters such as voltage, current, and bowtie filtration, for the primary dose calculation, we simulated the forward projection from the source to each voxel of an imaging object including some inhomogeneous inserts. Then we calculated the primary absorbed dose at each voxel based on the absorption probability deduced from the HU values and Beer's law. In sequence, all voxels constructing the phantom were regarded as secondary sources to radiate scattered photons for scattered dose calculation. Details of forward projection were identical to that of the previous step. The secondary source intensities were given by using scatter-to- primary ratios provided by NIST. In addition, we compared the analytically calculated dose distribution with their Monte Carlo simulation results.


RESULTS
The suggested framework for absorbed dose estimation successfully provided the primary and secondary dose distributions of the phantom. Moreover, our analytic dose calculations and Monte Carlo calculations were well agreed each other even near the inhomogeneous inserts.


CONCLUSION
This work indicated that our framework can be an effective monitor to estimate a patient's exposure owing to cone-beam CT scan for image-guided radiation treatment. Therefore, we expected that the patient's over-exposure during IGRT might be prevented by our framework.