Chemo-radiation treatment for GBM damages normal brain tissues and leads to significant deterioration in patients’ quality of life months or years after treatment. Magnetization transfer (MT) is sensitive to white matter damage and may detect it early. We observed significant reduction in MT exchange rate (RM0B) that quantifies white matters integrity as early as one month after 6-week chemo-radiation. The treatment impact on normal brain tissue was observed even in regions that received low radiation dose. More importantly, not all patients experienced MT reduction showing the heterogeneity of response to treatment and the potential of MT in identifying vulnerable patients.