Room: Exhibit Hall | Forum 1
Purpose: To obtain accurate anatomical information of tumor in motion and surrounding organ in patient at the timing of proton beam irradiation in Real-time-image Gated Proton Therapy (RGPT), 4-dimensional Cone Beam CT (4D-CBCT) technique based on fiducial marker-position was developed by applying dual-orthogonal fluoroscopic imaging system originally used for tumor tracking. This technique has features that it can treat not 2D-motion of tumor or surrounding organ like diaphragm on projection-images but 3D-motion of tumor directly, and it can monitor baseline shift of direction orthogonal to the body axis which is hard to recognize on projection-images. We report the initial phantom study to evaluate the effect of this technique.
Methods: Dynamic Thorax phantom (CIRS, Ltd) were used for this evaluation. Tumor-model Î¦1 cm and gild marker Î¦2 mm were activated in cosâ?´ wave function (SI/AP/RL = Amp. 10/ 5/ 0 mm, Cyc. 4/ 4/ 0 s). 3D marker-position was estimated according to its 2D coordinates on two set of the projection-images and each-image was separated according to the marker position if it enters the gating-area which one side is 4 mm of the cube (gating-separation). The projection-images were reconstructed by Feldkamp-Davis-Kress algorithm. As the comparison, image-quality and position-identification of motion object were evaluated for no separation, SI direction separation of 4mm length on 2D images and gating-separation.
Results: Motion artifacts on axial and sagittal plan were reduced only when we use gating-separation. Image degradation due to streak-artifact was observed, however, such a quality was enough to judge the position stability of tumor at the timing of patient positioning.
Conclusion: Proposed technique has the potential to obtain anatomical information of tumor in motion and surrounding organ. We will further investigate optimal reconstruction-methods to improve the CBCT quality and apply this technique to treatment procedure of RGPT.