Room: Stars at Night Ballroom 4
Purpose: To evaluate a total system uncertainty for frameless radiosurgery/therapy with the Gamma Knife Icon.
Methods: The Gamma Knife Icon treatment workflow was evaluated with various QA techniques. Included steps were patient positioning system (PPS) positioning, PPS stability, CBCT localization at stereotactic center, CBCT definition of stereotactic space, CBCT stability, MRI to CBCT registration, infrared fiducial motion management (IFMM) accuracy, mask immobilization, IFMM tracking during treatment, and residual IFMM motion post CBCT correction. The system related uncertainty was measured with QA phantoms, many of which provided by Elekta while the patient-related measurements were mined from the patient records and treatment log files of 30 treated patients. PPS and CBCT definition were measured using the Elekta film phantom treated at 100, 100, 100 first with defined tabled parameters and next with a CBCT-definition-defined shot position over the needle. CBCT definition was tested by offset of the phantom and registration with baseline for known offsets. Stability of PPS and CBCT were measured using the daily QA diode tool results. MRI to CBCT registration was evaluated with Target Registration Error methods from TG-132 on 10 patients. The IFMM log files, analyzed using a Python script for data extraction, provided the mask immobilization data of the IROC Head phantom during treatment and motion during treatment and uncorrected position after CBCT registration for 30 patients. (IRB 2017-0216)
Results: Total absolute vector mean for all sources of uncertainty, added in quadrature, was 1.30 (Â±0.52) mm. The mean error in each translational direction was also calculated to be 0.25 (Â±0.54), 0.34 (Â±0.57), and 0.54 (Â±0.64) mm in the X-, Y-, and Z-directions respectively.
Conclusion: For frameless treatment on the Gamma Knife Icon, the uncertainty seems to be quite small, but may not be under the 1 mm threshold traditionally believed to be attained by the frame-based treatment.