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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

Brachytherapy is the first conformal radiation therapy. A sealed source is placed in or in contact with the tumor providing dose to the tumor with small volumes of normal tissue irradiated. It became more sophisticated with the usage of remote afterloader. With this, our responsibility as physicists increased and became critical in ensuring an accurate and precise treatment planning and delivery. The ability to deliver a correct treatment is conditioned by the precision of the source placement at the dwell point/points predicted by the treatment planning system (TPS). The introducing of the CT based planning gave the possibility of reconstructing not only the correct shape of a treated volume but the correct reconstruction of the applicators, the catheters, and localizing the first dwell position (the stopping point) of the radioactive source that will deliver the treatment. The first condition of delivering a good and accurate treatment is correct catheter and applicators reconstruction, correct distance evaluation to each dwell position, and extremely good and well organized quality control program before the applicators and connectors are used and before the treatment plan is sent to the treatment console. This lecture will provide an introduction into the understanding of High Dose Radiation Therapy QA and commissioning of the applicators. It will provide detailed descriptions of the remote afterloader, applicators, and all the quality assurance tools necessary for organizing and running a safe and secure High dose radiation therapy program (HDR) in a cancer center. Learning Objective: 1. Understanding the HDR process: technical and practical 2. Understanding the importance of a well implemented quality assurance program 3. Understanding the different aspects of commissioning and calibrating of the radioactive source and the applicators used in HDR. 4. Challenges and solutions of running a HDR program in a cancer center

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