Sequential Diffusion Tensor Imaging and Magnetic Resonance Spectroscopy in Patients Undergoing Reirradiation for Progressive Diffuse Intrinsic Pontine Glioma

Abstract

Purpose: Diffusion tensor imaging for evaluation of white matter tracts is used with magnetic resonance spectroscopy (MRS) to improve management of diffuse intrinsic pontine glioma (DIPG). Changes in the 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 reirradiation for progressive DIPG. Here, we report a case series of 4 patients who received reirradiation 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. Methods and Materials: The median reirradiation dose was 25.2 Gy (24-30.8 Gy). Fiber tracking was performed using standard tractography analysis. The FA and ADC values for the corticospinal and medial lemniscus tracts were calculated before and after reirradiation. Multivoxel MRS was performed. Findings were correlated with clinical features and conventional MRI of tumors. Results: All patients had an initial response to reirradiation as shown by a decrease in tumor size. In general, FA increased with disease response and decreased with progression, whereas 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. The MRS analysis revealed a decrease in choline:creatinine and choline:N-acetylaspartate ratios during tumor response and increase during progression. Conclusions: Distinct changes in white matter tracts and tumor metabolism were observed in patients with DIPG undergoing reirradiation on a prospective clinical trial. Changes related to tumor response and progression were observed after 24 to 30.8 Gy reirradiation.