SU-E-T-402: Evaluation of the Accuracy of a Novel Open Mask System for Immobilization of Cranial Stereotactic Radiosurgery Patients




To evaluate the accuracy of a novel open mask for intracranial SRS and to investigate the capability of monitoring intrafraction motion of the patient within this mask using the optical surface monitoring system (OSMS) on a linac-based platform.


Efficiency was evaluated by measuring mask fabrication time during CT simulation and setup time in the treatment room. Mask shrinkage was assessed by comparing shim settings during treatment to simulation and also by measuring the distance between anterior and posterior sections of the mask on CBCT and Sim CT. Mask comfort was evaluated qualitatively post-treatment by surveying patients. Intrafraction motion was examined using 2D-3D autofusion of orthogonal kV images at mid-treatment. The intrafraction motion accuracy of the OSMS was analyzed by measuring the surface area of mask opening in Eclipse and pictures from the OSMS cameras.


The average preparation time for mask setup during simulation and treatment was 12.7 ± 2.3 min and 1.8 ± 0.9 min, respectively. Shims needed to be increased on average 0.8 mm, 0.8 mm, and 0.6 mm for right, left, and superior positions, respectively. CBCT measurements showed mask shrinkage, 0.8 mm both anteriorly and posteriorly. Greatest discomfort was reported on forehead followed by neck and chin. Intrafraction motion was less than 1 mm/1°. Accuracy of OSMS monitoring depended on the selected ROI. The OSMS monitored motion within 1 mm and 1° when the open surface area measured in Eclipse and captured by the camera > 147 cm2 and 33 cm2, respectively. When such conditions were not met, the accuracy somewhat degraded, an issue which can be mitigated by increasing the superior area or by angling the mask to expose greater surface to the camera.


The new mask system rigidly immobilizes with sub-mm accuracy during treatment according to optical camera (OSMS) measurements.

Research supported in part by a grant from QFix (Avondale, PA) and Varian Medical System (Palo Alto, CA)