Sequential diffusion tensor imaging and magnetic resonance spectroscopy in patients undergoing re-irradiation for progressive diffuse intrinsic pontine glioma

Abstract Purpose Diffusion tensor imaging (DTI) for evaluation of white matter tracts is used with magnetic resonance spectroscopy (MRS) to improve management of diffuse intrinsic pontine glioma (DIPG). Changes in apparent diffusion coefficient (ADC), fractional anisotropy (FA), and tumor metabolite ratios have been reported after initial radiation for DIPG, but these markers have not been studied sequentially in patients undergoing re-irradiation for progressive DIPG. Here, we report a case series of four patients who received re-irradiation for progressive DIPG on a prospective clinical trial in which we evaluated quantitative changes in FA, ADC, and tumor metabolites and qualitative changes in white matter tracts. Materials/Methods Median re-irradiation dose was 25.2 Gy (24-30.8 Gy). Fiber tracking was performed using standard tractography analysis. FA and ADC values for the corticospinal and medial lemniscus tracts were calculated pre- and post-reirradiation. Multivoxel MRS was performed. Findings were correlated with clinical features and conventional MRI of tumors. Results All patients had an initial response to re-irradiation as shown by a decrease in tumor size. In general, FA increased with disease response and decreased with progression while ADC decreased with disease response and increased with progression. At second progression, the FA fold change relative to values during disease response decreased in both patients with available imaging at second progression. Visualization of tracts demonstrated robust reconstitution of previously disrupted paths during tumor response; conversely, there was increased fiber tract disruption and infiltration during tumor progression. MRS analysis revealed a decrease in Cho:Cr and Cho:NAA ratios during tumor response and increase during progression. Conclusions Distinct changes in white matter tracts and tumor metabolism were observed in DIPG patients undergoing re-irradiation on a prospective clinical trial. Changes related to tumor response and progression are observed after 24-30.8 Gy re-irradiation.