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 near-infrared spectroscopy (fNIRS) can detect acute changes in brain functional signal variability during a single fraction of whole-brain radiotherapy (WBRT).&#xD;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 during the two radiation fields of a treatment fraction and in the time periods before, after, and between them. &#xD;Main results: Statistically significant irradiation associated changes were observed across all parameters in the VLF and full-band frequency ranges (p < .05). In these ranges, irradiation was associated with decreased fAPF and increased SE and CV. In the respiratory and cardiac frequency ranges, significant effects were observed primarily in fAPF and CV, with decreases in respiratory range fAPF and increases in cardiac range fAPF, while CV changes resembled those observed in the VLF and full band ranges. The temporal profiles differed between parameters; fAPF and SE had largest deviations in the interval between radiation fields, while CV increases were most pronounced during the radiation fields. Overall, the direction and magnitude of changes varied across parameters, highlighting complementary but non-uniform patterns of hemodynamic signal variability.&#xD;Significance: These findings demonstrate that fNIRS can detect immediate, irradiation-associated modulations in brain physiological pulsations during WBRT, suggesting its potential for early brain imaging-based monitoring of radiation induced functional changes.