200 Kv X-Ray Source For Radiotherapy And Imaging: Preliminary Results And Discussion

The system presented herein consists of a custom 200 kV electron tube with deflection magnets and stationary water-cooled targets for radiotherapy (RT) and imaging. The electron beam is deflected and dwelled along 41 discrete anode locations equally spaced by 1 cm in a line, at equivalent speeds of 1000 cm/s, to create a focused radiotherapy source. The treatment beam is collimated into a triangular polyhedron shape, producing a 4 cm focal spot at the isocenter and corresponding planning-treatment-volume (PTV). This beam shape would allow entry dose to be distributed over large areas for skin sparing. The source is mounted on a ring gantry that rotates at speeds up to 1.5 rpm. Preliminary dose rate measurements were collected in air at 140 kV beam energy, up to 80 mA beam current. Radiographic film was used to collect an image of the treatment beam at isocenter. Results are presented and can be extrapolated to a dose rate of 2 Gy/min for a 140 kV, 200 mA beam. The electron beam can be deflected within 1 ms from therapy path to an additional array of 19 imaging targets, which provides hardware capabilities for real-time tomosynthesis and image-guided RT. Onboard cone beam CT for patient positioning is also available. The utilization of 200 kV beam treatment energies compared to MV greatly reduces the required shielding (4-6 mm lead vs. 1-2 m concrete) and the cost of radiotherapy system installations. Systems can be mounted onto standard mobile trailers for use at remote locations.