Performance of a Novel Frameless and Maskless Robotic Head Motion Compensation System for Stereotactic Radiosurgery in a Realistic Clinical Environment with Healthy Volunteers.

Purpose: Stereotactic radiosurgery (SRS) is a non-surgical method for treating brain abnormalities and small tumors. Traditional high-accuracy SRS requires a rigid metal head frame screwed into the skull, which causes discomfort and reduces patient compliance. Thermoplastic masks offer a less invasive alternative but compromise accuracy due to flexing and are often still uncomfortable. To address these issues, we developed a novel robotic head motion compensation (RHMC) device that enables frameless and maskless SRS.

Methods: A compact, portable RHMC device was developed that can be quickly attached to or detached from the end of a linear accelerator (Linac) treatment table. Real-time 6D head position tracking was performed using 3D surface-guided radiation therapy (SGRT) imaging, which was fed into the robot control computer. Device performance was evaluated by administering virtual SRS treatments to a phantom, and 20 healthy volunteers, simulating a clinical environment but without delivering radiation. The primary success metric was defined as maintaining the 6D target position under a 1.0mm and 1.0deg threshold for more than 95% of beam-on time (denoted as DC95%_1.0mm&1.0deg).

Results: Two of the 20 volunteers were excluded due to incompatibility with the RHMC device. Among the remaining 18 volunteers, the DC95%_1.0mm&1.0deg success metric was achieved in all cases. Without RHMC, 9 of the 18 volunteers were able to meet this metric. For a tighter tolerance of DC95%_1.0mm&0.5deg, 17 volunteers achieved the metric with RHMC, compared to 4 without. For a tolerance of 1.0mm&1.0deg, across all 18 volunteers, the mean and range were 99% and 96-100% using RHMC, respectively, compared to 73% and 9-100% without RHMC.

Conclusions: The RHMC device effectively maintained accurate head motion control under simulated clinical conditions, achieving the DC95%_1.0mm&1.0deg success metric for all suitable candidates. This technology has the potential to enable frameless and maskless SRS delivery within or better than current standard-of-care tolerance guidelines.