WE‐A‐BRA‐03: Towards Real‐Time Ultrasound Image‐Guided Abdominal Radiotherapy

Purpose: Accurate tumor positioning in stereotactic body radiotherapy of abdominal lesions is often hampered by organ motion and set‐up errors. The problems of the daily variation (interfractional motion) in tumor position can be partially corrected with on‐line soft‐tissue image‐guided radiotherapy. However, a greater challenge is to also capture the movement during treatment (intrafractional motion). Methods: To study the feasibility of abdominal real‐time volumetric soft‐tissue image‐guidance with ultrasound (US) imaging, we are investigating several aspects each with their own challenges: 3DUS volumetric imaging, 2DUS time series of the organ motion, robotic US probe placement, US auto‐contouring and contrast enhanced US (CEUS). Results: Currently, 3DUS imaging is used first to correct for the set‐up errors as well as interfractional organ motion. One of the conditions for reliable and accurate results in this part is acquiring US images without artifacts due to breathing motion. For interfractional corrections, this can be realized by imaging during breath hold. In order to track intrafractional tumor and organ motion, including breathing induced, we are moving towards acquisition of temporal 3D image series. As an interim step, we discuss acquisition of temporal 2D datasets. As opposed to prostate, where the US probe can be placed on the perineum during treatment to avoid interaction with the radiation beam, the probe positions required for liver are more complex. Therefore, we are developing robot‐ assisted positioning of the probe. Not all abdominal lesions are clearly visible on US images. By introducing CEUS, more tumors will have increased contrast allowing tracking them. With real‐time tumor tracking it is impossible to manually delineate structures. Therefore auto‐contouring algorithms for this specific application are under investigation. Conclusion: By combining all the investigated technologies we aim to develop a reliable real‐time volumetric soft‐tissue US image‐guidance system for clinical implementation. Research sponsored by ElektaLearning Objectives:1‐ understand the challenges of in‐vivo real time motion monitoring2‐ understand the role of ultrasound imaging in in‐vivo real time motion monitoring3‐learn about our efforts to develop a system for ultrasound‐ based in‐vivo real time motion monitoring.