An oblique arc capable patient positioning system for sequential tomotherapy

A new patient positioning system has been designed and manufactured, allowing for the accurate delivery of obliquely oriented intensity modulated treatment arcs via a commercially available IMRT system. The ability to deliver such obliquely oriented intensity modulated arcs allows the commercial system to more closely approach a 4pi pencil beam delivery geometry which, in turn, allows for significant improvements in conformality for many tumor geometries. While the IMRT system delivered to this institution in the fall of 1996 was capable of planning for nonparallel plane delivery schemes, it proved incapable of delivering such treatments with acceptable accuracy. Because our early clinical experience revealed that certain patients could benefit significantly from such a delivery scheme we endeavored to design and manufacture an alternative treatment couch/patient positioning system (Xlator) which could overcome the limitations of the vendor supplied system. We present our initial evidence for the benefits of obliquely oriented intensity modulated treatment arcs, along with data demonstrating the inability of the original vendor supplied system to deliver such treatments with acceptable accuracy. The design of our new system is presented, as well as data demonstrating its ability to accurately deliver obliquely oriented intensity-modulated arcs. A detailed comparison of the performance of the Xlator and the vendor-supplied system is presented with regard to match line repeatability and hysteresis. Finally, the ability of the Xlator to deliver multiple couch angle sequential tomotherapy with spatial accuracy necessary to radiosurgical applications is demonstrated via a AAPM Report 54,TG-42 hidden target test. Readers note: The Xlator patient positioning system designed and patented here has recently come to be commercially available, and is currently marketed by the vendor under the name Crane II.