Heidelberg 2006 – scientific programme

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ST: Strahlen- und Medizinphysik

ST 11: Verbesserung der Bestrahlungsplanung

ST 11.7: Talk

Tuesday, March 14, 2006, 17:50–18:00, D

Linac based kV cone-beam CT for extended field-of-views — •Annette Seeber, Simeon Nill, Thomas Tücking, and Uwe Oelfke — Deutsches Krebsforschungszentrum, Medizinische Physik (E040), INF 280, 69120 Heidelberg

In our approach towards adaptive radiotherapy the patient anatomy is imaged directly prior to the treatment with a linac-integrated kV cone-beam CT system. The 3D-reconstruction field-of-view (FOV) is currently restricted to 26cm at isocenter due to the size of available flat panel imagers (FPIs). The acquisition of imaging data for larger patient volumes can be realised with a laterally shifted FPI. A Feldkamp-based reconstruction algorithm was modified to account for this asymmetric detector setup by a weighting operation on the projections prior to filtered back-projection.

Following successful simulations with synthetic projection data, experiments were performed with humanoid phantoms and special contrast phantoms, using different detector offsets corresponding to FOVs of up to 48cm. The achieved image quality was analysed as a function of the detector offset and the distance from the central slice by comparison with images obtained from our normal cone-beam setup and from a diagnostic CT scanner.

The achievable FOV increase permits the use of the existing cone-beam CT system also for extra-cranial regions, retaining good image quality for structure matching and adaptive therapy planning.