Purpose: Present a non-gantry solution by utilizing isocentric rotating chair as a patient positioner to provide non-planar fields of carbon-ion beam on treating Patients of Head and Neck cancer at seating position.
Methods: Multiple fixed-beamline carbon-ion fields in patientâ€™s sagittal plane provided clinical acceptable target doses with carbon-ion high dose-gradient and enhanced radiobiological effectiveness. However, non-planar fields could achieve better dose-sparing of organs-at-risk. To have non-coplanar fields, a non-gantry solution of isocentric rotating chair can be equivalently to a heavy/expensive gantry solution. A robot with serial-join manipulators was initially considered. Observed interference between the long robot arm and the patientâ€™s leg rest require a complex movement mechanism under the seat. Therefore, the concept of parallel kinematics was adapted to manufacture the prototype chair, it has 20-degree angle-tilt over 360-degree rotation over a 500 mm cubic treatment volume. A compact assembling including a Stewart hexapod platform and independent 360-degree rotation and 3D translation can be completely placed under the seat. By utilizing modern 3D-design visual tool with industrial fine-element simulation of material stress under various loads of weight, this approach shows better and efficient way to build any precise mechanical device instead of using a wood mocked model.
Results: Mechanical accuracy of each module and fully assembled chair was first evaluated by using a laser dynamic tracking system. The, the accuracy to execute required displacement by image-guidance positioning system was performed in a clinic treatment workflow. Positioning accuracy of 0.8mm and 0.6-degree was achieved during the integration of rotating chair to position a head phantom with a tile angle up to 5-degree.
Conclusion: With achieved mechanical accuracy of chair itself and an integration of clinical workflow, the rotating chair provides better incident angles of radiation field for carbon-ion beam in a fixed beamline for treating patients with head and neck cancer.