ESTRO 37 Abstract book

S1106

ESTRO 37

before clinical application of RTRT using kV image with 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.

Results The relative differences of pixel values were 0.44 ± 0.22, 0.30 ± 0.13, and 0.11 ± 0.09% for 4,6 and 10 MV, respectively. The difference between fiducial marker position in actual and simulated image were 0.005 ± 0.002(LR), 0.060 ± 0.005(SI), 0.014 ± 0.004(AP) mm for 4MV, 0.011 ± 0.012(LR), 0.060 ± 0.003(SI), and 0.006 ± 0.006(AP) mm for 6 MV, and, 0.008 ± 0.009(LR), 0.067 ± 0.011(SI), and 0.026 ± 0.026(AP) for 10 MV. The differences of TMS were 0.10 ± 2.06% (-1.48%−3.10%), 4.88 ± 0.31% (4.54%−5.27%) and 2.54 ± 1.58% (0.26%−3.63%) for 4, 6 and 10 MV. Conclusion We have developed the simulation system to evaluate the tracking accuracy using kV imaging with MV scatter. It was suggested that it was possible to evaluate the tracking accuracy using this system. To archive RTRT with high dose rate, it is needed to evaluate the tracking accuracy in clinical case using this system. EP-2022 Interlay effect in SBRT VMAT lung FFF treatments using ionization liquid chambers array detector J. Bonaque-Alandi 1 , J. Bonaque-Alandi 2 , J.A. Bautista- Ballesteros 3 , J.A. Bautista-Ballesteros 2 , B. Ibanez- Rosello 2 , M. Adria-Mora 2 , J. Gimeno-Olmos 2 , V. Carmona- Meseguer 2 , F. Lliso-Valverde 2 , J. Perez-Calatayud 2 1 consorcio Hospitalario Provincial De Castellón, Radiofísica Y Proteccion Radiológica, Catellón De La Plana, Spain 2 hospital Universitario Y Politécnico La Fe, Oncología Radioterápica, Valencia, Spain 3 hospital Institut Curie, Radiotherapy, Paris, France Purpose or Objective To evaluate the interplay effect in SBRT VMAT lung treatments with flattering filter (FF) and flattering filter free (FFF) beams using a ionization liquid chambers array detector. Material and Methods Eight plans of different patients with 4D computed tomography (4DCT) were used in which each phase was used to generate the internal target volume (ITV). To create the treatment planning volume (PTV), expansion ITV 5 mm in all directions was done. For all cases, two

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.