Purpose: Aim of this study is to evaluate the compatibility of robotic couch assisted six-dimensional (6D) patient positioning systems with external independent imaging modalities for two different accelerators, Varian and Elekta.
Methods: In both machines integrated image guidance systems like cone-beam CT (CBCT) provide patient set-up errors that can be corrected by the respective 6-D couch. Additionally, in-room image guidance systems (BrainLAB’s ExacTrac) can be integrated into the workflow to provide pre-, post, and intrafraction set-up errors. Varian 6 degrees of freedom (DoF) couch, comprises three translational axes (x, y, z), table column’s rotational axis (yaw). Pitch and roll rotations are done by the couch’s bellows. After 6-D correction, couch remains physically rotated about the vertical axis (yaw: zROT? 0). In Elekta’s HexaPOD 6 DoF couch, the column rotational axis is not in the 6 DoF. HexaPOD’s bellows can execute all three rotations (pitch, roll, and yaw) and the 3D couch movements are limited to the translational axes. All positional corrections are isocenter focussed.
Results: Varian's way of correcting the rotational error in yaw direction makes it partially incompatible with in-room ExacTrac. In case patient’s 6D setup correction is initiated with delta shifts obtained from in-room imaging, the resultant finite zROT inhibits incorporation of CBCT in the subsequent workflow. On the other hand, if the patient’s 6-D setup correction is initiated from Varian’s CBCT, the resultant zROT in subsequent stereoscopic in-room imaging would reflect as a deviation from planned rotation values. However, in Elekta, since zROT occurs only for the 6-D couch top without involving any column rotation, it is possible to flip between or combine the CBCT and the in-room imaging any time during the workflow.
Conclusion: One of the commercially available 6-D robotic couch solutions (Varian) is only partially compatible with the independent in-room imaging system.
Cone-beam CT, Acceptance Testing, Dual-energy Imaging
Not Applicable / None Entered.