Distinguishing Tumor Admixed in a Radiation Necrosis (RN) Background: 1H and 2H MR With a Novel Mouse Brain-Tumor/RN Model

Purpose: Distinguishing radiation necrosis (RN) from recurrent tumor remains a vexing clinical problem with important health-care consequences for neuro-oncology patients. Here, mouse models of pure tumor, pure RN, and admixed RN/tumor are employed to evaluate hydrogen (H-1) and deuterium (H-2) magnetic resonance methods for distinguishing RN vs. tumor. Furthermore, proof-of-principle, range-finding deuterium (H-2) metabolic magnetic resonance is employed to assess glycolytic signatures distinguishing RN vs. tumor. Materials and Methods: A pipeline of common quantitative H-1 MRI contrasts, including an improved magnetization transfer ratio (MTR) sequence, and H-2 magnetic resonance spectroscopy (MRS) following administration of H-2-labeled glucose, was applied to C57BL/6 mouse models of the following: (i) late time-to-onset RN, occurring 4-5 weeks post focal 50-Gy (50% isodose) Gamma Knife irradiation to the left cerebral hemisphere, (ii) glioblastoma, growing similar to 18-24 days post implantation of 50,000 mouse GL261 tumor cells into the left cerebral hemisphere, and (iii) mixed model, with GL261 tumor growing within a region of radiation necrosis (H-1 MRI only). Control C57BL/6 mice were also examined by H-2 metabolic magnetic resonance. Results: Differences in quantitative H-1 MRI parametric values of R1, R2, ADC, and MTR comparing pure tumor vs. pure RN were all highly statistically significant. Differences in these parameter values and DCEAUC for tumor vs. RN in the mixed model (tumor growing in an RN background) are also all significant, demonstrating that these contrasts-in particular, MTR-can effectively distinguish tumor vs. RN. Additionally, quantitative H-2 MRS showed a highly statistically significant dominance of aerobic glycolysis (glucose -> lactate; fermentation, Warburg effect) in the tumor vs. oxidative respiration (glucose -> TCA cycle) in the RN and control brain. Conclusions: These findings, employing a pipeline of quantitative H-1 MRI contrasts and H-2 MRS following administration of H-2-labeled glucose, suggest a pathway for substantially improving the discrimination of tumor vs. RN in the clinic.

Automated summary

In this study, a pipeline of quantitative H-1 MRI contrasts and H-2 MRS was used to distinguish radiation necrosis (RN) from tumor. The results showed that the quantitative H-1 MRI parametric values and MTR can effectively differentiate between RN and tumor. Additionally, the H-2 MRS results revealed a significant difference in glucose metabolism between tumor and RN.