SU‐G‐JeP1‐11: Feasibility Study of Markerless Tracking Using Dual Energy Fluoroscopic Images for Real‐Time Tumor‐Tracking Radiotherapy System

Purpose: The new real‐time tumor‐tracking radiotherapy (RTRT) system was installed in our institution. This system consists of two x‐ray tubes and color image intensifiers (I.I.s). The fiducial marker which was implanted near the tumor was tracked using color fluoroscopic images. However, the implantation of the fiducial marker is very invasive. Color fluoroscopic images enable to increase the recognition of the tumor. However, these images were not suitable to track the tumor without fiducial marker. The purpose of this study was to investigate the feasibility of markerless tracking using dual energy colored fluoroscopic images for real‐time tumor‐tracking radiotherapy system. Methods: The colored fluoroscopic images of static and moving phantom that had the simulated tumor (30 mm diameter sphere) were experimentally acquired using the RTRT system. The programmable respiratory motion phantom was driven using the sinusoidal pattern in cranio‐caudal direction (Amplitude: 20 mm, Time: 4 s). The x‐ray condition was set to 55 kV, 50 mA and 105 kV, 50 mA for low energy and high energy, respectively. Dual energy images were calculated based on the weighted logarithmic subtraction of high and low energy images of RGB images. The usefulness of dual energy imaging for real‐time tracking with an automated template image matching algorithm was investigated. Results: Our proposed dual energy subtraction improve the contrast between tumor and background to suppress the bone structure. For static phantom, our results showed that high tracking accuracy using dual energy subtraction images. For moving phantom, our results showed that good tracking accuracy using dual energy subtraction images. However, tracking accuracy was dependent on tumor position, tumor size and x‐ray conditions. Conclusion: We indicated that feasibility of markerless tracking using dual energy fluoroscopic images for real‐time tumor‐tracking radiotherapy system. Furthermore, it is needed to investigate the tracking accuracy using proposed dual energy subtraction images for clinical cases.