Linac-Based Accelerated Volume-Staged Radiosurgery for Large Avms: Planning Framework and Reported Outcomes
Abstract
Purpose
To present our institution’s LINAC-based accelerated volume-staged stereotactic radiosurgery (AVS-SRS) planning strategy and outcomes for large (≥6 cc), high-risk cerebral AVMs, where surgical resection and trans-arterial embolization were technically or clinically inadvisable or resulted in no change
Methods
Nineteen patients underwent simulation CT, CT angiography (CTA), magnetic resonance angiography (MRA), and cerebral arteriography. Imaging datasets were co-registered in Varian Eclipse and Brainlab Angio Element software to assist collaborative nidus delineation by a radiation oncologist and neurosurgeon. Large AVMs were subdivided into 2–3 anatomically distinct sub-targets (3–4 cc each), prioritizing individual angioarchitecture and proximity to critical structures over arterial feeding or venous drainage patterns. Sub-targets were treated sequentially with 2–3-week interstage intervals, delivering a cumulative prescription dose of 16–24 Gy at the 80% isodose line to the entire nidus. Non-coplanar IMRT/VMAT planning prioritized optimal sub-target coverage, minimized dose spillage, maximized conformity index (CI), minimized gradient index (GI), and limited brain V12 Gy. Individual-stage and composite plan isodoses and DVHs were iteratively assessed during planning to meet AVS-SRS plan quality criteria and adjust if needed. Treatments were delivered on a stereotactic-dedicated LINAC equipped with HD-MLC, six-degree-of-freedom couch, IGRT, and SGRT.
Results
Thirteen patients (68.4%) were treated in two stages and six (31.6%) in three stages. Median sub-target volumes were 4.29 ± 2.84 cc, 3.99 ± 2.73 cc, and 4.75 ± 3.56 cc. Complete resolution occurred in 7 patients (36.8%), partial response in 11 (57.9%); one patient was unevaluable. Symptomatic radiation necrosis occurred in three patients (15.8%), with no significant differences observed between patients with and without necrosis in nidus volume, CI, GI, or V12 (p > 0.05). No post-AVS-SRS hemorrhage occurred.
Conclusion
LINAC-based IMRT/VMAT AVS-SRS with short interstage intervals is a feasible treatment for large cerebral AVMs, achieving favorable obliteration rates with low symptomatic necrosis and no post-treatment hemorrhage.