Evaluation of MRI-Guided Linear Accelerator Based Stereotactic Radiosurgery for Brain Metastasis
M De Ornelas*, N Dogan, W Amestoy, H Guerrero, T Diwani, E Mellon, Sylvester Comprehensive Cancer Center, University of Miami, Miami, FL
Presentations
SU-IePD-TRACK 6-7 (Sunday, 7/25/2021) 5:30 PM - 6:00 PM [Eastern Time (GMT-4)]
Purpose: Assess the feasibility of an MRI-guided linac system in treating brain metastasis by comparing the plan quality to a frameless automated linac-based SRS system for treatment of brain metastasis.
Methods: Ten patients with a single metastatic lesion were retrospectively planned using a frameless automated linac-based SRS planning system with HDMLC (2.5mm leaf-width) and an MRI-guided linac system with double-focused double-stacked multileaf collimator (4.15mm leaf-width). Lesion sizes ranged from 0.3cc to 27.1cc, with an average of 5.1cc. Energy for all plans was 6MV FFF and normalization set to cover 99.5% of the target volume with the prescription dose. The HDMLC plans utilized VMAT technique with 4-5 non-coplanar arcs at 1200 MU/min while the MRI-guided linac system used step-and-shoot technique with multiple coplanar beams at 600 MU/min. Plan quality was assessed by the following metrics: gradient index (GI), RTOG conformity index (CI(R)(T)(O)(G)), brain volume receiving 12Gy or more (V12Gy) and maximum dose (D(m)(a)(x)) for brainstem, optic chiasm, and optic nerves. Two-sided Wilcoxon sign-rank test (statistical significance at p<0.05) was used to test differences between metrics.
Results: All plans met OAR constraints. D(m)(a)(x) to the brainstem, optic chiasm and nerves were not significantly different between the plans. HDMLC-linac plans were statistically better in terms of GI (p=0.00), CI(R)(T)(O)(G) (p=0.00) and V12 (p=0.01).
Conclusion: Our study demonstrates that MRI-guided linac system can provide comparable organs-at-risk sparing to the HDMLC-linac for treatment of single metastatic lesions, although the HDMLC-linac plans had better GI, CI(R)(T)(O)(G), and V12. The GI for the MRI-guided plans improved with increasing target volumes, achieving acceptable values (<4.0) for targets greater than 3cc, suggesting it could be used for SRS treatment of single metastasis targets larger than this size.
ePosters
Keywords
Stereotactic Radiosurgery, MRI, Line Spread Function
Taxonomy
TH- External Beam- Photons: intracranial stereotactic/SBRT
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