Functional Magnetic Resonance Imaging-Guided Stereotactic Radiosurgery to Avoid Symptomatic Radionecrosis

Functional magnetic resonance imaging (fMRI) localizes eloquent areas of the brain more accurately than structural imaging alone and minimizes the risk of neurosurgical injury. However, fMRI remains underutilized in stereotactic radiosurgery (SRS). We assessed the neuroanatomic relationship between SRS to brain metastases (BMs), nearby eloquent areas, identified using fMRI, and attributable symptoms of radionecrosis (RN). We then evaluated the advantage of a novel fMRI-guided SRS (fMRI-SRS) planning approach.

Patients with an fMRI study within 3 months of SRS for BMs were included. The nearest eloquent area (NEA) was defined as the motor, language, or visual eloquent area on fMRI nearest to an irradiated BM. The primary outcome was focal symptomatic RN (FSRN), defined as radiographic RN with progressive neurologic symptoms localizable to the NEA. The relationship between dose to the NEA and risk of FSRN was assessed with logistic regression. Cases were replanned using fMRI-SRS, maximizing NEA avoidance while maintaining target coverage.

Among 93 patients, 76 (82%) had resection prior to SRS. The most common SRS prescription was 30 Gy in 5 fractions. The NEA was a motor eloquent area in 71 cases (76%) and a language area in 18 cases (19%). Of 20 patients who developed radiographic RN, 4 (20%) were asymptomatic, 4 (20%) had nonlocalizable neurologic symptoms, and 12 (60%) had focal neurologic symptoms directly attributable to the NEA, consistent with FSRN. Among patients who received 5-fraction SRS with modern planning techniques, greater V14Gy (single-fraction equivalent) to the NEA predicted increased risk of FSRN at 18 months (odds ratio, 6.8/mL; P= .05). fMRI-SRS reduced NEA V14Gy in all cases replanned, with a mean reduction of 22.5%.

Focal neurologic symptoms of RN reflect SRS dose to nearby eloquent areas on fMRI. fMRI-SRS planning minimizes dose to eloquent areas without sacrificing target coverage and may mitigate neurologic toxicity.