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Initial Setup Accuracy Comparison Between Frame-Based and Frameless Stereotactic Radiosurgery

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T Tseng

T Tseng*, R Sheu , B Todorov , S GREEN , S Blacksburg , Y Lo , Mount Sinai Medical Center, New York, NY


TH-A-9A-5 Thursday 7:30AM - 9:30AM Room: 9A

Purpose:To evaluate initial setup accuracy for stereotactic radiosurgery (SRS) between Brainlab frame-based and frameless immobilization system, also to discern the magnitude frameless system has on setup parameters.

Methods:The correction shifts from the original setup were compared for total 157 SRS cranial treatments (69 frame-based vs. 88 frameless). All treatments were performed on a Novalis linac with ExacTrac positioning system. Localization box with isocenter overlay was used for initial setup and correction shift was determined by ExacTrac 6D auto-fusion to achieve submillimeter accuracy for treatment. For frameless treatments, mean time interval between simulation and treatment was 5.7 days (range 0-13). Pearson Chi-Square was used for univariate analysis.

Results:The correctional radial shifts (mean±STD, median) for the frame and frameless system measured by ExacTrac were 1.2±1.2mm, 1.1mm and 3.1±3.3mm, 2.0mm, respectively. Treatments with frameless system had a radial shift >2mm more often than those with frames (51.1% vs. 2.9%; p<.0001). To achieve submillimeter accuracy, 85.5% frame-based treatments did not require shift and only 23.9% frameless treatment could succeed with initial setup. There was no statistical significant system offset observed in any direction for either system. For frameless treatments, those treated ≥ 3 days from simulation had statistically higher rates of radial shifts between 1-2mm and >2mm compared to patients treated in a shorter amount of time from simulation (34.3% and 56.7% vs. 28.6% and 33.3%, respectively; p=0.006).

Conclusion:Although image-guided positioning system can also achieve submillimeter accuracy for frameless system, users should be cautious regarding the inherent uncertainty of its capability of immobilization. A proper quality assurance procedure for frameless mask manufacturing and a protocol for intra-fraction imaging verification will be crucial for frameless system. Time interval between simulation and treatment was influential to initial setup accuracy. A shorter time frame for frameless SRS treatment could be helpful in minimizing uncertainties in localization.

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