Program Information
Dedicated Cone-Beam Breast CT: Design of a 3-D Beam-Shaping Filter
S Vedantham, L Shi*, A Karellas, University of Massachusetts Medical School, Worcester, MA
Presentations
TU-CD-207-10 (Tuesday, July 14, 2015) 10:15 AM - 12:15 PM Room: 207
Purpose: To design a 3-D beam-shaping filter for cone-beam breast CT for equalizing x-ray photon fluence incident on the detector along both fan and cone angle directions.
Methods: The 3-D beam-shaping filter was designed as the sum of two filters: a bow-tie filter assuming cylindrical breast and a 3D difference filter equivalent to the difference in projected thickness between the cylinder and the real breast. Both filters were designed with breast-equivalent material and converted to Al for the targeted x-ray spectrum. The bow-tie was designed for the largest diameter cylindrical breast by determining the fan-angle dependent path-length and the filter thickness needed to equalize the fluence. A total of 23,760 projections (180 projections of 132 binary breast CT volumes) were averaged, scaled for the largest breast, and subtracted from the projection of the largest diameter cylindrical breast to provide the 3D difference filter. The 3-D beam shaping filter was obtained by summing the two filters. Numerical simulations with semi-ellipsoidal breasts of 10-18 cm diameter (chest-wall to nipple length=0.75 x diameter) were conducted to evaluate beam equalization.
Results: The proposed 3-D beam-shaping filter showed a 140%-300% improvement in equalizing the photon fluence along the chest-wall to nipple (cone-angle) direction compared to a bow-tie filter. The improvement over bow-tie filter was larger for breasts with longer chest-wall to nipple length. Along the radial (fan-angle) direction, the performance of the 3-D beam shaping filter was marginally better than the bow-tie filter, with 4%-10% improvement in equalizing the photon fluence. For a ray traversing the chest-wall diameter of the breast, the filter transmission ratio was >0.95.
Conclusion: The 3-D beam shaping filter provided substantial advantage over bow-tie filter in equalizing the photon fluence along the cone-angle direction. In conjunction with a 2-axis positioner, the filter can accommodate breasts of varying dimensions and chest-wall inclusion.
Funding Support, Disclosures, and Conflict of Interest: Supported in part by NIH R01 CA128906 and R21 CA134128. The contents are solely the responsibility of the authors and do not reflect the official views of the NIH or NCI.
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