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The Utilization of Isocentric Rotating Chair in Fixed Carbon-Ion Beamline to Treat Patients of Head and Neck Cancer at Seating Position: Mechanical Implementation of Hexapod-Based Patient Positioner

W Hsi1*, R Zhou2 , X Zhang2 , F Yang2 , Z Wang2 , Y Sheng3 , J sun3 , (1) University Florida Health Proton Therapy Institute, Jacksonville, FL, US (2) College of Physical Science and Technology,Sichuan University, Chengdu, China(6) Shanghai Proton and Heavy Ion Center, Shanghai, ,(7) shanghai proton and heavy ion center, Shanghai, China


(Sunday, 7/14/2019) 1:00 PM - 2:00 PM

Room: 302

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 patient’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 patient’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.


Radiation Therapy, Heavy Ions, Treatment Techniques


TH- External Beam- Particle therapy: Carbon ion therapy - instrumentation

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