Effect of residual patient motion on dose distribution during image-guided robotic radiosurgery for skull tracking based on log file analysis

The present study aimed to assess the effect of residual patient motion on dose distribution during intracranial image-guided robotic radiosurgery by analyzing the system log files. The dosimetric effect was analyzed according to the difference between the original and estimated dose distributions, including targeting error, caused by residual patient motion between two successive image acquisitions. One hundred twenty-eight treatments were analyzed. Forty-two patients were treated using the isocentric plan, and 86 patients were treated using the conformal (non-isocentric) plan. The median distance from the imaging center to the target was 55 mm, and the median interval between the acquisitions of sequential images was 79 s. The median translational residual patient motion was 0.1 mm for each axis, and the rotational residual patient motion was 0.1A degrees for Delta pitch and Delta roll and 0.2A degrees for Delta yaw. The dose error for D (95) was within 1 % in more than 95 % of cases. The maximum dose error for D (10) to D (90) was within 2 %. None of the studied parameters, including the interval between the acquisitions of sequential images, was significantly related to the dosimetric effect. The effect of residual patient motion on dose distribution was minimal.