München 2004 – scientific programme

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ST: Strahlenphysik und Strahlenwirkung

ST 3: Biomedizinische Bildgebung III

ST 3.1: Fachvortrag

Monday, March 22, 2004, 16:30–16:45, HS 129

4D Computed Tomography for Treatment Planning — •Eike Rietzel and George Chen — Massachusetts General Hospital, Department of Radiation Oncology, 30 Fruit St, Boston, MA, 02114, USA

Advanced beam delivery techniques in radiotherapy, like scanned particle beams or IMRT, allow to increase the conformity between target and irradiated volume. Besides patient setup, achievable conformity is limited by inter- and intrafractional organ motion. Intrafractional organ motion is mainly caused by respiration.

To study organ motion, we have begun the acquisition of time-resolved Computed Tomography scans. In conventional Computed Tomography scans, respiratory motion can cause significant artifacts. Four-dimensional Computed Tomography significantly reduces such artifacts. To obtain temporal information, at each couch position data are acquired in axial cine scan mode for the duration of the patient’s respiratory cycle. Several images per couch position are reconstructed, each representing a different point in time within the respiratory cycle. Images from different couch positions are then sorted into several spatio-temporal coherent CT volumes.

4DCT results in several volumetric datasets throughout the respiratory cycle. Such data allow analysis of tumor and organ motion. Target segmentation is significantly improved due to the reduction of motion artifacts. To ensure dose coverage throughout the respiratory cycle, combined target volumes can be generated from targets segmented at different respiratory phases. Furthermore, the impact of respiratory motion on dose distributions can be studied.