Purpose: Current stereotactic radiosurgery (SRS) methods employ invasive head frames/masks for patient immobilization. To overcome these issues, we have developed a frameless/maskless robotic SRS system using 6DoF parallel kinematic robotics to control patient head motion throughout the SRS delivery process at the sub-millimeter and sub-angular level. To verify the dosimetric accuracy of the system, we report on end-to-end phantom tests utilizing both Gafchromic film and NIPAM gel dosimetry.
Methods: An in-house built 6DoF robotic platform was used to simulate prior recorded 6D head motion of several volunteers. This data was collected using a real-time infrared 6DoF motion tracking camera. Standard single and multi-target SRS treatment plans were developed for evaluation using anthropomorphic phantom studies for static, simulated volunteer motion, and robotically stabilized cases. In addition, NIPAM gel dosimeters that can be read out using CT imaging were created in-house, and a phantom was developed to fix them to the robotics during irradiation.
Results: Preliminary film results suggest better dose agreement between the static and robotically stabilized case (3%/3 mm; Γ= (90.06±7.43)% and 1%/1 mm; Γ= (65.03±20.75)%) than the static and simulated motion case (3%/3 mm; Γ= (85.23±5.57) % and 1%/1 mm; Γ= (52.12±9.63)%). However, the 5 mm spacing between Gafchromic films does not resolve small targets and the small cavity volume of the CIRS phantom does not allow accurate simulation of single isocenter multi-target therapy. To overcome these limitations, we are currently in the process of repeating the experiment with NIPAM gels.
Conclusion: The robotic platform was used to simulate human head motion for dosimetric evaluation of the system. Results suggest stacked film dosimetry does not have the necessary spatial resolution for comprehensive 3D dose analysis. It is anticipated the higher 3D spatial dose resolutions offered by the NIPAM gel will allow better resolving of small SRS targets.
Stereotactic Radiosurgery, Film, Gel Dosimeter