AbstractID: 9678 Title: An analytical approach to prevent gantry-couch collision for linac-based radiosurgery

ID: 9678 Title: An analytical approach to prevent gantry-couch collision for linac-based radiosurgery Gantry-couch collision is a serious concern for the treatment planning of the linac-based stereotactic radiosurgery (SRS). The ability to detect collision at the planning time removes the need for backup plans and preserves the useful beam angles that would be deemed unsafe and discarded otherwise. Most collision-detection schemes guard only against the most apparent collisions. A fool-proof collision-map requires detailed measurement of machine geometry and complex graphic operations. In this study, we propose a simple analytical method for collision detection using machine-specific data. Gantry and couch parts are modeled as cubic or cylindrical objects, which are geometrically defined by the coordinates of eight corners for cubic objects, and by five parameters for cylindrical objects. The collision problem is mathematically solved by determining whether any physical dimensions of the couch and gantry approach each other closer than an allowed limit. A computer code was implemented and tested on a Varian Clinac 600C linac equipped with a BrainLab micro-MLC. The coordinates of couch and collimator objects were first measured at the origin of the patient BRW coordinate system. They were subsequently translated and rotated to study the clearance of various beam arrangements. The predicted collision schemes were verified at the machine. Our method correctly predicted the collision map for a retrospective study of ten previously-treated SRS plans. It also accurately predicted the collisions for all five artificially created setup conditions. In conclusion, we have developed an analytical method for SRS collision detection that is easy to implement, computationally inexpensive, and accurate.