3154 - Quantifying the Impact of Intrafraction Patient Motion on Target Coverage in Frameless Gamma Knife Stereotactic Radiosurgery Using CBCT-Derived Rigid Transformations
Presenter(s)
N. Ud Din1, R. Kotecha1,2, R. H. Press1,2, D. J. Wieczorek1,2, Y. Lee1,2, M. D. Hall1,2, E. Bander3,4, M. W. McDermott3,4, M. P. Mehta1,2, A. Gutierrez1,2, and R. P. Tolakanahalli1,2; 1Department of Radiation Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, FL, 2Department of Oncological Sciences, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, 3Department of Neuroscience, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, 4Department of Neurosurgery, Miami Neuroscience Institute, Baptist Health South Florida, Miami, FL
Purpose/Objective(s):
High-definition motion management (HDMM) system uses an infrared camera tracking a nasal reference marker to provide submillimeteric (0.1-0.15mm) real-time tracking and pausing (based on pre-specified thresholds) for frameless Gamma Knife (GK) stereotactic radiosurgery (SRS). HDMM assumes that nasal motion is equivalent to or exceeds tumor motion, but how well small HDMM-detected nose-marker displacements translate into clinically meaningful target coverage loss (?TC), particularly for small or peripheral lesions, is unclear. This study investigated the impact of intrafraction motion on changes on ?TC.Materials/Methods:
Consecutive patients treated with frameless GK SRS using mask immobilization (2017-2024) at a tertiary-care institution were included. For fractions with =1 mid-treatment CBCT, 4×4 rigid transformation matrices (TM) were extracted from the GK database. Intrafraction motion was calculated from the rigid TM calculated between the pre-treatment CBCT and mid-treatment CBCT and reported. Additionally, three hypothetical lesion-location groups (superior, central, inferior) of varying sizes (3, 5, 8,10, 15 mm) were planned to 22 Gy/1fx with 100% TC. Representative patient-derived TMs were proportionally rescaled to simulate stereotactic-space motion corresponding to HDMM nose-marker displacement of 0.5-, 1.0-, and 1.5-mm and applied to planned shot coordinates to quantify ?TC.Results: A total of 188 patients (225 treatment courses) met inclusion criteria. Across all CBCT pairs, isocenter-corrected absolute translations (median [IQR]) were X: 0.74 [0.47-1.25] mm, Y: 0.50 [0.21-1.11] mm, and Z: 0.96 [0.48-1.21] mm; rotations were 0.20° [0.09-0.31]°, 0.14°[0.07-0.24]°, and 0.16°[0.09-0.31]° about the x-, y-, and z-axes respectively. ?TC (median [range]) were 0.1% [0.0-0.8%], 0.2% [0.0-9.0%] and 0.7% [0.0-20.6%] for simulated HDMM tolerances of 0.5 mm,1.0 mm and 1.5 mm with the largest changes observed for smaller and peripherally located targets.
Conclusion:
Despite tight HDMM tolerances (=1.5 mm), small rotational components can produce spatially amplified displacement for lesions farther from the stereotactic center, increasing target coverage loss. Central lesions were less affected, whereas peripheral targets particularly those <8 mm diameter were more sensitive supporting need for location/size specific PTV margins and HDMM tolerances.