Functional diffusion map: A biomarker of brain metastases response to treatment based on magnetic resonance image analysis

Validated biomarkers for treatment response in patients suffering from brain metastases are needed in daily clinical practice as they may improve survival by providing reliable prognostic information and allowing alternative therapies. This work presents a new analysis tool for an early and non-invasive evaluation of treatment response in patients with brain metastases. A set of twenty-five metastases from sixteen patients were examined by T1-weighted and diffusion magnetic resonance imaging before starting radiotherapy and at least once after treatment. Diffusion MRI can show a correlation between water diffusion variation within metastasis area and its clinical evolution. Images were co-registered to pretreatment scans. Diffusion changes, resulting in spatially varying changes in apparent diffusion coefficient values of metastatic lesions, were quantified and presented as a functional diffusion map (fDM). These functional maps were compared to two traditional criteria for assessing oncological response. Of the twenty-five metastases analyzed, seven were classified as partial response (PR), eight as stable disease (SD) and nine as progressive disease (PD). Normalized volume values of the metastases for each response group were obtained, disclosing that apparent diffusion coefficient increase was a good predictor of response. Sensitivity was 88%, specificity 100%, positive predictive value 100% and negative predictive value was 94%. Outcome reveals that the implemented tool, based on functional diffusion mapping as evolution biomarker, provides a reliable prediction of metastases response to treatment.