Functional near-infrared spectroscopy reveals frequency-specific brain pulsation changes during whole-brain radiotherapy

Objective: Radiotherapy is widely used to treat brain tumors and metastases, but many survivors experience long-term cognitive dysfunction. Recent evidence suggests that central nervous system damage may occur earlier than previously recognized. We studied whether functional nearinfrared spectroscopy (fNIRS) can detect acute changes in variability of brain function during a single fraction of whole-brain radiotherapy (WBRT). Approach: We recorded fNIRS signals from 30 patients (n=90 fractions) during WBRT. From these signals we analyzed fractional amplitude of physiological fluctuations (fAPF), spectral entropy (SE), and coefficient of variation (CV) across very low frequency (VLF < 0.1 Hz), respiratory (0.13–0.6 Hz), cardiac (0.6–5 Hz), and full-band frequency bands. Parameters were calculated for oxygenated and deoxygenated hemoglobin, and water signals before, during, between, and after radiation fields of a treatment fraction. Main results: The results showed statistically significant irradiation induced changes in all parameters in VLF and full band frequencies (p < .05). Additionally, differences were seen in fAPF and CV in respiratory and cardiac frequencies (p < .05). Changes varied in direction and effect size between parameters. Significance: Acute changes in brain physiological pulsations were detected using fNIRS during WBRT, suggesting its potential for early monitoring of radiation-induced changes in brain function.