Perfusion MRI of the brain after radiotherapy in patients with glioblastoma – potential and problems

Sammanfattning: Perfusion Magnetic Resonance Imaging (MRI) is a useful tool in diagnostic evaluation and treatment response assessment in patients with glioblastoma. The standard treatment regimen includes surgical resection, radiotherapy and adjuvant chemotherapy. However, prognosis is poor; relative 5-year survival is 3–5%. Radiotherapy sequelae may have considerable negative effects on the patients’ quality of life. Acute and early delayed radiation-induced injury is primarily considered damage to the cerebral vascular tissue. The general aim of this study was to evaluate how perfusion MRI evaluation, based on contrast agent administration (DSC- and DCE-MRI), is affected by or can be useful to assess radiation-induced changes in normal appearing brain tissue in patients with glioblastoma after radiotherapy. Paper I: Dynamic Susceptibility Contrast (DSC)-MRI is a common perfusion MRI method in clinical practice in patients with glioblastoma. Due to inherent limitations, cerebral blood volume (CBV) and cerebral blood flow (CBF) derived from DSC-MRI are normalized to contralateral normal appearing white matter. Ten patients with glioblastoma were examined. Regional and global normalized CBV and normalized CBF in white and gray matter decreased after radiotherapy, followed by a tendency to recover. The response of nCBV and nCBF was dose-dependent in white matter but not in gray matter. In conclusion, radiotherapy effects on normal appearing white matter can confound treatment evaluation with DSC-MRI in patients with glioblastoma. Paper II: Dynamic Contrast Enhanced (DCE)-MRI may be useful in evaluating radiation-induced damage in normal appearing brain tissue.  DCE-MRI-derived parameters, vascular permeability (Ktrans) and the fractional volume of the extravascular extracellular space (Ve) are potential biomarkers. Twelve patients with glioblastoma were examined. A tendency toward increased Ktrans and Ve was seen, suggesting that these parameters may act as potential biomarkers for acute and early delayed radiation-induced vascular damage