Berlin 2008 – wissenschaftliches Programm

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ST: Fachverband Strahlen- und Medizinphysik

ST 5: Heavy Ion Therapy and Related Basic Research I

ST 5.5: Vortrag

Dienstag, 26. Februar 2008, 10:30–10:45, H 2033

Accuracy of a 3D online motion compensation system for tumor therapy with scanned ion beams — •Nami Saito¹, Christoph Bert¹, Naved Chaudhri¹, Alexander Schmidt¹, Dieter Schardt¹, and Eike Rietzel^1,2 — ¹GSI, Darmstadt, Germany — ²Siemens Medical Solutions, Erlangen, Germany

An integrated three-dimensional online motion compensation (3DOMC) system is being developed at GSI to treat tumors in moving organs with scanned ion beams. Target motion is detected by a laser distance sensor, and the motion compensation parameters are calculated in a dedicated module of the treatment control system (TCS). The lateral compensation parameters are sent to the TCS controller of the scanning magnets to adapt the beam laterally. The longitudinal compensation parameters are sent to a range shifter which consists of two sets of PMMA wedges mounted on linear motors. The wedges are placed symmetrically to form a double wedge with a homogeneous thickness in the overlapped area. By moving the wedges apart or together with the linear motors the range of the traversing ion beams can be modulated.

The system response time has been optimized to ≈ 1 ms for lateral compensation and to ≈ 25 ms for 5 mm water equivalent depth compensation. In experiments with a position detector deviations of 0.3 mm RMS were measured for lateral motion compensation by comparing measured and nominal beam positions. For longitudinal compensation an accuracy of 0.2(2) mm was obtained by comparing stationary depth dose profiles to those with motion compensation.