Simulation of intrafraction motion and overall geometrical accuracy of a frameless intracranial radiosurgery process

Abstract

Comprehensive evaluation of clinical accuracy of an image-guided frameless intracranial radiosurgery system was performed. All links in the process chain were tested. A novel method was evaluated on healthy volunteers to prospectively quantify the range of target motion for optimal PTV margin determination. The overall system isocentric accuracy was tested with a rigid anthropomorphic phantom containing a hidden target. Intrafraction motion was simulated in five healthy volunteers. Head and shoulders reinforced thermoplastic masks were used for immobilization. The subjects were placed in a treatment position for 15 minutes (the maximum expected time between repeated isocenter localizations) and the six-degree-of-freedom target displacements were recorded with high frequency by tracking infrared markers. The markers were placed on a customized piece of thermoplastic secured to the head independently of the immobilization mask. Additional data were collected with the subjects holding their breath, talking, and deliberately moving. The automatic registration algorithm did not introduce clinically significant errors compared to fiducial matching (