Oct 01

QP 28 - Radiation and Cancer Physics 14: Image-guided Planning, Novel Delivery Techniques and QA

1162 - Obliteration with Preservation: Functional MRI as a Critical Adjunct in Optimizing Radiosurgical Outcomes for Eloquent AVMs

12:05pm - 12:10pm PT

Room 160

Presenter(s)

Vangipuram Shankar, MD, MBBS - Apollo Proton Cancer Centre, Chennai , Tamil Nadu

V. Shankar¹, S. Ghosh², S. Cholayil¹, R. Adhityan³, K. P. Srinivasan Paramasivam⁴, A. S. Uday Krishna⁵, and R. Jalali⁵; ¹Apollo Cancer Centers, Chennai, India, ²Dept. of Neurosurgery, Apollo Proton Cancer Center, Chennai, India, ³Department of Radiology, Apollo Proton Cancer Center, Chennai, Chennai, India, ⁴Endovascular Neurosurgery, Apollo Hospitals, Greams Road, Chennai, India, ⁵Apollo Proton Cancer Centre, Chennai, India

Purpose/Objective(s): Stereotactic radiosurgery (SRS) is cornerstone treatment for motor-eloquent region AVMs. Conventional SRS planning lacks functional mapping, increasing risk for radiation-induced motor deficits. f-MRI addresses this by mapping motor cortex activity. Study evaluates fMRI’s impact on (1) targeting accuracy (2) toxicity reduction (3) functional preservation.

Materials/Methods: Single-arm retrospective study included 23 patients (2015–2023) with supratentorial AVMs =5 mm from fMRI-defined motor cortex (Spetzler-Martin Grade II–IV).

AVM characteristics included median nidus volume of 4.2 cm³ (IQR: 2.1–6.7) locations spanning precentral gyrus (n=15), supplementary motor area (n=5), and thalamocortical motor pathways (n=3). Imaging included 3T MRI (T1-post-contrast, T2-FLAIR, TOF), 3D rotational angio (Biplane cathlab) and fMRI.

Functional MRI (fMRI) performed using a block-design motor task paradigm tailored to AVM location (finger-tapping or foot dorsiflexion) to activate the primary motor cortex with pre-scan rehearsal for compliance. Blood oxygen level-dependent (BOLD) signals which detect hemodynamic changes in active motor regions during task performance, were analyzed using SPM12 with activation thresholds set at p<0.001 (family-wise error corrected).

fMRI maps coregistered with MRI/ 3D - Rotational Angio - planning CT for nidus delineation while fMRI-defined motor regions were outlined as critical avoidance structures

Treatment prioritized >95% nidus coverage (>18-20 Gy/1 SF or 37.5gy / 5fr. for AVM's close to critical areas or measuring >3cm) while restricting motor cortex to <10 Gy/1fr.or 18.75gy/5frc. Dose gradients were optimized to fall off rapidly (= 2 Gy/mm) near functional zones and all treatment delivered on a frameless robotic radiosurgery system using skull tracking.

Patients underwent serial MRI and clinical evaluations at 6-month intervals for the first 2 years, then annually. DSA was performed at 3 years or if MRI suggested residual flow. Primary endpoints: Nidus obliteration (DSA-confirmed absence), Radiation necrosis (MR perfusion criteria), and motor deficits (MRC =4/5).

Results: At median 4.1-year follow-up, obliteration was 78.3% (18/23; 95% CI:58.1–90.3%), with 83.3% (15/18) for AVMs =3 cm vs. 60% (3/5) for >3 cm. Symptomatic radiation necrosis occurred in 4.3% (1/23; seizures) and asymptomatic necrosis in 8.7% (2/23). Motor deficits occurred in 4.3% (1/23; 9.5 Gy to motor cortex). Hypofractionated SRS (n=5) achieved 80% obliteration (4/5) without toxicity. Nidal coverage >95% with 18 Gy correlated with higher obliteration (87.5% vs. 57.1%, p=0.09). With Motor cortex median max dose:8.4 Gy (IQR:7.1–9.3) no deficits were seen.

Conclusion: f-MRI-guided SRS achieved 78.3% obliteration with minimal morbidity, demonstrating efficacy-safety balance. Hypofractionation optimized outcomes for large AVMs. fMRI enables precise cortical sparing, enhancing therapeutic ratios and is recommended for motor-eloquent AVMs.