Room: Exhibit Hall
Purpose: To report on the clinical assessment of cone-beam CT (CBCT) patient alignment procedures in particle therapy and to quantify the discrepancies of the 6 degrees of freedom (DOF) set-up correction indications obtained from a double X-ray two-dimensional orthogonal setup verification versus three-dimensional CBCT.
Methods: In particle therapy, a standard approach for inter-fraction setup verification encompasses the matching of orthogonal X-ray images acquired before irradiation to the reference digitally reconstructed radiographs coming from the planning CT.At our facility, a custom solution for in-room X-ray imaging was implemented to perform 2D/3D patient registration from orthogonal projections and 3D/3D alignment using CBCT.Patients included in this study were imaged and repositioned according to 2D\3D registration of bony structures. A subsequent CBCT acquisition was performed to include also soft tissue information, thus resulting in the estimation of a second setup correction vector. Automatic 3D\3D registration was performed excluding any further manual alignment and any region of interest selection.CBCT-based registration residuals of 60 patients (July 2014-February 2018; 440 acquisitions) were analyzed. Head and neck (3 cases, 27 acquisitions), and Extra-cranial (57 cases, 413 acquisitions) treatment sites have been analyzed separately.
Results: Median values (interquartile) of the 6 DOF correction vectors are expressed as lateral (LL), superior-inferior (SI), anterior-posterior (AP) translations and rotation around vertical (ROT), transverse (PITCH) and sagittal (ROL) axis. All results are reported in [mm] and [Â°]. Extra-cranial: 0.09(0.88); 0.04(0.57); -0.04(0.89); 0.01(0.06); -0.01(0.10); 0.04(0.10); maximum recorded value in AP direction (-14.98 mm). Head and neck: -0.01(0.47); 0.02(0.89); -0.15(0.35); 0.00(0.01); 0.00(0.02); 0.03(0.04); maximum recorded value in SI direction (2.08 mm).
Conclusion: Setup residuals after CBCT registration procedures confirm the importance of a conscious choice of adequate imaging verification systems. According to tumor site, maximum residual setup deviations were found to be lower when imaged structures were less influenced by organ motion.
Not Applicable / None Entered.