CEST contrasts remain stable in normal-appearing brain tissues but reveal tumor-specific alterations after radiotherapy in glioma patients

Motivation: Routine MRI struggles to differentiate tumor progression from treatment-induced changes in glioma patients after chemoradiotherapy (CRT). Chemical exchange saturation transfer (CEST) yields metabolic information and could support a reliable differentiation. Goal(s): To explore potentially different CEST contrast changes in normal-appearing brain tissue and gliomas after CRT. Approach: Prospective clinical trial of 3 Tesla CEST MRI before CRT (photons and protons) and up to seven months thereafter. Results: CEST contrasts remain unchanged in white and gray matter that received up to 60 Gray. However, CEST contrasts change inside gliomas, and the APT-weighted contrast develops differently in progressive versus non-progressive tumors. Impact: CEST contrasts remain unchanged in normal-appearing brain tissue after radiotherapy but change inside gliomas. Based on these findings, CEST contrast changes in gliomas after radiotherapy should be considered to be tumor-specific, and may be used to support tumor response assessment.