Room: AAPM ePoster Library
Purpose: is extremely critical to have accurate localization of target in stereotactic space for stereotactic radiosurgery (SRS) treatment. The introduction of the newest Gamma Knife Icon?? allows for multiple methods to define stereotactic space. This includes via frame fiducials defined by MRI, frame fiducials defined by CT, or patient location defined by CBCT. However, there is no direct comparison on the accuracy of these methods. This study is designed to evaluate the variation of different methods to define stereotactic space with Gamma Knife Icon??.
Methods: each patient selected, the stereotactic reference was re-defined using: (M1)fiducials in CT registered to MRI;(M2)fiducials in MRI;(M3)CBCT registered to MRI;(M4)CBCT registered to CT then to MRI. The transformation matrix correlating MRI to stereotactic reference and shot positions were recorded. Thirty target positions were randomly created within a 15-cm diameter spherical space centered at the stereotactic center. Shot positions defined by each method were calculated by applying the transformation matrix to target positions. Shot positions defined by M1 was taken as the reference. The shot position variation (SPV) relative to M1 was evaluated.
Results: total of 8 patients were included in this retrospective study. The mean (range) of SPV was 0.64 mm (0.08-1.91 mm), 0.64 mm (0.17-1.66 mm) and 0.31 mm (0.00-0.83 mm) for M2, M3 and M4 respectively. No statistical difference of SPE was observed between M2 and M3. The SPV for M4 was significantly lower than M2 and M3 (p < 0.05, paired T-test).
Conclusion: methods resulted in different stereotactic space definition. Though in general within sub-millimeter range, some shot position variations beyond 1 mm were observed. The data also suggested to acquire an additional CT when using CBCT to define stereotactic space and when registering to MRI to localize the target. This action can help mitigate targeting errors for Gamma Knife based-radiosurgery.
Not Applicable / None Entered.