Finite element analysis of a capacitive array for 6D intrafraction motion detection during stereotactic radiosurgery

This work presents a non-contact, non-ionizing solution for the continuous detection and characterization of intrafraction cranial motion with six-degrees of freedom (DoF). This capacitive monitoring system is a modular tool capable of detecting the cranial position through a thermoplastic mask without the use of skin as a surrogate. The purpose of this investigation is to develop an array of capacitive monitoring sensor plates capable of detecting translational and rotational cranial motion during radiotherapy. This study compares the performance of different capacitive monitoring array designs for their potential to detect intrafraction cranial translations and rotations. To this end, a finite element analysis (FEA) model of the human cranium was used to calculate the system capacitance while simulating translational (superior-inferior, lateral, anterior-posterior) and rotational (roll, pitch, yaw) cranial motion. The model was validated by comparing simulation results against experimental results acquired with the help of human volunteers. The verified FEA model was then used to compare multiple potential array designs. The arrays' sensitivities to translational and rotational motion and uniqueness of response were compared to determine the most promising design for six-DoF motion detection. The most promising array design was chosen for a clinical volunteer study.