This study explores the volumetric reconstruction fidelity attainable using tomosynthesis with a kV imaging system which has a unique ability to rotate isocentrically and with multiple degrees of mechanical freedom. More specifically, we seek to investigate volumetric reconstructions by combining multiple limited‐angle rotational image acquisition sweeps. By comparing these reconstructed images with those of a CBCT reconstruction, we can gauge the volumetric fidelity of the reconstructions. In surgical situations, the described tomosynthesis‐based system could provide high‐quality volumetric imaging without requiring patient motion, even with rotational limitations present. Projections were acquired using the Digital Integrated Brachytherapy Unit, or IBU‐D. A phantom was used which contained several spherical objects of varying contrast. Using image projections acquired during isocentric sweeps around the phantom, reconstructions were performed by filtered backprojection. For each image acquisition sweep configuration, a contrasting sphere is analyzed using two metrics and compared to a gold standard CBCT reconstruction. Since the intersection of a reconstructed sphere and an imaging plane is ideally a circle with an eccentricity of zero, the first metric presented compares the effective eccentricity of intersections of reconstructed volumes and imaging planes. As another metric of volumetric reconstruction fidelity, the volume of one of the contrasting spheres was determined using manual contouring. By comparing these manually delineated volumes with a CBCT reconstruction, we can gauge the volumetric fidelity of reconstructions. The configuration which yielded the highest overall volumetric reconstruction fidelity, as determined by effective eccentricities and volumetric contouring, consisted of two orthogonally‐offset 60° L‐arm sweeps and a single C‐arm sweep which shared a pivot point with one the L‐arm sweeps. When compared to a similar configuration that lacked the C‐arm component, it is shown that the C‐arm improves the delineation of volumes along the transverse axis. The results described herein suggest that volumetric reconstruction using multiple, unconstrained orthogonal sweeps can provide an improvement compared with traditional cone beam CT using standard axial rotations.PACS number: 87.57.nf

No abstract

No abstract

Purpose: To retrospectively compare dose prescription for MammoSite RTS using single versus multiple reference points through DVH evaluation. Method and Materials: CT images of four women treated with MammoSite RTS were selected for a retrospective study of dose prescription. The balloon was identified and contoured on the CT images using Plato BPS. A PTV was created by volumetrically expanding the balloon volume by 1cm. The final volume, PTV_EVAL consisted of the PTV minus the balloon volume. Six reference points were added along the outside edge of PTV_EVAL. Four points were added at locations lateral to the axis of the catheter, and two points were added along the axis of the catheter. Dose was prescribed to the six points individually, and DVHs of PTV_EVAL were calculated. Then dose was prescribed to 4, 5, and 6 reference points simultaneously, and a new DVH was created for each of those three cases. Results: For each prescription, the V150, V100, V90 and D95 from the DVH for PTV_EVAL were recorded and averaged across the four patients. When dose was prescribed individually to the two points along the catheter axis, the tissue volume receiving excess dose was unacceptable. When dose was prescribed individually to the 4 points lateral to the catheter axis, the coverage became inadequate. Plans in which dose was prescribed to multiple points simultaneously displayed sufficient coverage with lower volumes receiving excess dose. Conclusion: Due to the anisotropy of the source, prescriptions to individual points resulted in unacceptable coverage of the target volume or excess dose to tissue, while prescribing to multiple points simultaneously resulted in both more acceptable coverage and lower volumes of tissue receiving excess dose. Using four lateral points and one axial point resulted in the most target coverage while still limiting excess dose to tissue.

No abstract