Objective: To investigate the association between the magnetic resonance imaging (MRI) signal characteristics of skull base chordoma and radiosurgical outcomes. Methods: Twenty-four patients with skull base chordomas treated with Gamma Knife radiosurgery (GKRS) after previous surgical resection were retrospectively (2001–2021) examined. Pre-GKRS MRIs were analyzed for RT2 (tumor-to-brainstem signal intensity ratio on T2-weighted imaging), RCE (tumor-to-brainstem signal intensity ratio on contrast-enhanced T1-weighted imaging), and mean apparent diffusion coefficient (ADC). Correlations of the parameters with patient survival and local tumor progression were made by using Cox regression and Kaplan–Meier analyses. Results: During a median follow-up of 46 months after GKRS, 9 patients died with significantly more local tumor progression events (median number: 2 vs 0, P =.012) than did 15 alive patients. On multivariable analysis, higher mean ADC was associated with longer patient survival (P =.016) after GKRS. The actuarial 5-year overall survival rates were 88.9% versus 54.7% for chordomas with an ADC of ≥ 1270 × 10–6 mm2/s versus < 1270 × 10–6 mm2/s. RT2 < 1.5 (P =.038) and RCE > 1.57 (P =.022) were associated with a lower probability of local tumor control. Conclusion: Lower mean ADC values are associated with shorter patient survival in skull base chordomas after GKRS. Diffusion-weighted imaging may help in GKRS planning and outcome prediction for these patients.
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