Abstract Book

S1103

ESTRO 37

MV scatter. The purposes of this study were to develop the simulation system to evaluate the tracking accuracy using kV imaging with MV scatter and to verify this system. Material and Methods The simulation system consists of three processes (Fig.1). First, the log files and kV images acquired using SyncTraX in clinical case were prepared. Second, simulated images were calculated by adding measured MV scatter to kV images. Finally, clinical situations were reproduced using simulated images and log files and a fiducial marker were tracked using simulation system. Then, template matching score (TMS) and 3D fiducial marker coordinates were analyzed to evaluate tracking accuracy using new log files.

Conclusion PTV margins for DIBH RT for locally advanced NSCLC changed ~1mm after analysing a larger cohort of patients. This validation study highlights the necessity of designing PTV margins in large and representative patient cohorts. EP-2021 Simulation system for evaluating the tracking accuracy toward RTRT using kV imaging with MV scatter T. Shiinoki 1 , T. Uehara 2 , H. Hanazawa 1 , S. Kajiki 3 , Y. Mishina 4 , K. Shibuya 1 1 Yamaguchi University, Department of Radiation Oncology, Ube, Japan 2 Yamaguchi University Hospital, Department of Radiological technology, Ube, Japan 3 Shimadzu Corporation, Research & Development Department- Medical Systems Division, Kyoto, Japan 4 Shimadzu Corporation, Global Marketing Department- Medical Systems Division, Kyoto, Japan Purpose or Objective We have archived respiratory-gated radiotherapy using the real-time tumor-tracking radiotherapy (RTRT) system; SyncTraX developed by Shimadzu for lung and liver cancer. SyncTraX consists of two color image intensifiers and x-ray tubes. Using color fluoroscopic images acquired along two directions, the 3D coordinates of a fiducial marker close to a tumor is calculated. The kV imaging of SyncTraX with MV beam delivery on linac will be able to allow for RTRT during a treatment delivery with high- dose rate. However, tracking accuracy must be evaluated before clinical application of RTRT using kV image with

To verify this system, the experiments were performed (Fig 2). Actual simultaneous kV and MV images were measured using linac and SyncTraX for acrylic phantom. A fiducial marker with a diameter of 2.0 mm were placed at a depth of 8 cm. Photon energy were 4, 6, and 10 MV. Gantry angles were 0, 90, 180, 270. Field size was 15 x 15 cm 2 . As the same matter, kV and MV scatter image acquired separately. Simulated simultaneous kV and MV images were calculated using image processing. Static fiducial marker was tracked for actual and simulated images using developed simulation system. Simulated images were compared with actual imaging using calculated (1) mean ± S.D. of pixel values (2) fiducial marker position, and (3) TMS for each image.