Meeting the demands of highly precise Ion Beam Therapy - how a flat-panel detector can improve conformance tests

Radiotherapy with scanned particle beams enables a highly precise dose conformity to the target region while surrounding healthy tissue is widely spared. This leads to increased demands on the verification of the applied parameters of the beam and treatment plans. In several studies the potential of the commercially available amorphous silicon flat-panel detector RID 256-L (Perkin Elmer, Germany), originally designed for photon imaging, to meet these demands, and to simplify, fasten and extend clinically required conformance tests was investigated. The experiments were performed at the Heidelberg Ion Beam Therapy Center HIT, which employs a synchrotron and a raster scanning technique for patient treatments with proton and carbon ion beams. At HIT daily tests of the beam parameters including spot position, spot width and homogeneity of a scanned field are performed. A direct comparison with the currently used radiographic films showed that the flat-panel detector offers an adequate alternative to films, while being substantially faster. Furthermore, the detector was used to measure the water equivalent thickness of different samples and to obtain a high-resolution carbon ion computed tomography employing an energy scanning technique. This method offers a powerful tool to evaluate the performance of treatment planning algorithms by studying beam range uncertainties. The presented studies show that the investigated flat-panel device allows to enhance the acquired information in ion beam verification measurements and provides high spatial resolution, sensitivity and speed. It is therefore highly attractive to be used in measurements meeting the clinical needs.