ESTRO 36 Abstract Book

S876 ESTRO 36 _______________________________________________________________________________________________

Radiooncology and Radiotherapy, Aachen, Germany 2 Institute of Applied Medical Engineering RWTH Aachen University, Department of Rehabilitation- & Prevention Engineering, Aachen, Germany 3 RWTH Aachen University Hospital, Department of Nuclear Medicine, Aachen, Germany 4 Institute for Experimental Molecular Imaging RWTH Aachen University, Department of Physics of Molecular Imaging Systems, Aachen, Germany 5 European Institute for Molecular Imaging EIMI, University of Munster, Münster, Germany 6 Boll Automation GmbH, Research and Development, Kleinwallstadt, Germany 7 RWTH Aachen University, III. Institute of Physics B, Aachen, Germany Purpose or Objective For precise stereotactic radiation of lung tumours the exact position of the tumour has to be known. A common method for the detection of the tumour position is using fluoroscopy during treatment. This leads to a very precise tracking of the tumour position, but also causes additional dose in the scanned region. In this work an alternative solution to determine the actual tumour position without additional radiation is introduced. Combined information from FDG-PET scans and an accelerometer based system are used for a patient specific tumour movement prediction. Material and Methods We measured the breathing motions of ten patients in a clinical trial by placing six tri-axial accelerometers on the patient’s thorax and abdomen. Each patient is instructed to breathe in up to five different breathing techniques: ‘free breathing’, ‘deep thoracic’, ‘flat thoracic’, ‘deep abdominal’ and ‘flat abdominal’. Simultaneously, a FDG- PET scan was performed to correlate the patient’s respiratory states with the tumour positions afterwards. Retrospectively the tumour trajectory was extracted from the PET raw data and afterwards correlated with the information obtained by the accelerometers. The extraction of the respiratory motion was performed using the methods described in [1] and [2]. A verification of the motion extraction algorithm was performed with an in-house developed moving phantom. Results The measurements show a good agreement between real and reconstructed phantom motion. An analysis of a 'deep abdominal' breathing is shown in figure 1. The tumour trajectories are displayed in blue and the low pass filter of the data in red. Combining the information from the accelerometer system and the tumour trajectories a model can be obtained to predict the most likely tumour position for a given accelerometer signal [3]. Figure 2 shows the tumour trajectory in superior-inferior direction of a ‘free breathing’ instruction in blue and the predicted trajectory in orange. The model shows a good prediction of the real tumour trajectory.

Figure 1: Tumour trajectory (blue) and low pass filter (red)

Figure 2: Tumour trajectory (blue) and prediction (orange) Conclusion The algorithm for the tumour trajectory reconstruction was validated in this work . The presented data show a good agreement of the reconstructed and predicted tumour motion. Thus the accelerometer based system provides the opportunity for tumour tracking from breathing induced motion. Acknowledgment The work was funded by the Federal Ministry of Education and Research BMBF, KMU-innovativ, Förderkennzeichen: 13GW0060F. Reference [1] Detection of respiratory tumour motion using intrinsic list mode-driven gating in positron emission tomography, Florian Büther et al, Eur J Nucl Med Mol Imaging (2010) [2] Data-Driven Respiratory Gating Approach for Detecting Anterior-Posterior Tumor Motion in PET, M. Heß et al, IEEE (2016) [3] Evaluation und Verbesserung eines Systems zum Tracking von Organbewegungen, Jonatan H. Zeidler, Master Thesis, TU Ilmenau (2016) EP-1620 The immobilizing effect of the vacuum cushion in spinal SBRT and the impact of pain A.S. Gerlich 1 , J.M. Van der Velden 1 , G. Fanetti 2 , A. Zoetelief 1 , W.S.C. Eppinga 1 , E. Seravalli 1 1 University Medical Center Utrecht, Radiation Oncology, Utrecht, The Netherlands 2 European Institute of Oncology, Radiation Oncology, Milan, Italy Purpose or Objective The number of patients treated with spinal SBRT is increasing rapidly. This technique requires accurate dose delivery for the optimal treatment effect and protection of organs at risk (e.g. spinal cord). Accuracy can be