AbstractID: 9445 Title: Integrated Radiotherapy Imaging System (IRIS): Considerations
of tumor tracking with gantry-mounted kilovoltage x-ray systems
The design of an Integrated Radiotherapy Imaging System (IRIS) consisting of gantry mounted diagnostic (kV) x-ray tubes and flatpanel amorphous-silicon detectors has been studied. The system is designed for three main functions: simultaneous orthogonal
radiographs for 3D patient setup (with fluoroscopic capability for 4D patient setup/treatment), cone-beam C.T., and real-time tumor
tracking. The IRIS is unique in its integration of all three functions with the therapy linac. The goal of the current study is to determine
the optimal configuration of the IRIS. Some considerations include, the number of x-ray source/panel pairs and the position of each
relative to other sources, panels, and the linac beam’s isocenter. We have conducted a theoretical study of a single x-ray source/panel
pair using real patient data. Tumor localization is attempted for several beams/fractions in seven patients whose tumors exhibit 3dimensional motion greater than 1 cm peak-to-peak. In this study, we assumed the best-case scenario where 3-dimensional
fluoroscopic data is acquired during a training phase just prior to the first treatment fraction. Our results show that a monoscopic
system is inadequate for consistent real-time tumor tracking. Therefore, the IRIS will comprise of two x-ray source/panel pairs
mounted on the linac gantry. The placement of the x-ray sources/panels has been studied based on the geometric specifications of the
Varian 21EX Clinac. The locations selected minimize the measurement errors while maintaining a large field of view and avoiding
collisions with the floor and couch.
Research supported by Varian Medical Systems, Inc.