Towards MRI Differentiation of Recurring Tumor from Delayed Radiation Necrosis
Carlos J Perez-Torres, John A Engelbach, Jeremy Cates, Dinesh K Thotala, Robert E Drzymala, Joseph JH Ackerman, and Joel R Garbow Department of Radiology, Washington University in Saint Louis, Saint Louis, Missouri, United States, Department of Radiation Oncology, Washington University in Saint Louis, Saint Louis, Missouri, United States, Department of Chemistry, Washington University in Saint Louis, Saint Louis, Missouri, United States
A novel murine model for localized radiation necrosis and its characterization using advanced magnetic resonance imaging.
PURPOSE
To develop a murine model of radiation necrosis using fractionated, subtotal cranial irradiation; and to investigate the imaging signature of radiation-induced tissue damage using advanced magnetic resonance imaging techniques.


METHODS AND MATERIALS
Twenty-four mice each received 60 Gy of hemispheric (left) irradiation in 10 equal fractions. Magnetic resonance images at 4.7 T were subsequently collected using T1-, T2-, and diffusion sequences at selected time points after irradiation. After imaging, animals were killed and their brains fixed for correlative histologic analysis.


RESULTS
Contrast-enhanced T1- and T2-weighted magnetic resonance images at months 2, 3, and 4 showed changes consistent with progressive radiation necrosis. Quantitatively, mean diffusivity was significantly higher (mean = 0.86, 1.13, and 1.24 microm(2)/ms at 2, 3, and 4 months, respectively) in radiated brain, compared with contralateral untreated brain tissue (mean = 0.78, 0.82, and 0.83 microm(2)/ms) (p < 0.0001). Histology reflected changes typically seen in radiation necrosis.


CONCLUSIONS
This murine model of radiation necrosis will facilitate investigation of imaging biomarkers that distinguish between radiation necrosis and tumor recurrence. In addition, this preclinical study supports clinical data suggesting that diffusion-weighted imaging may be helpful in answering this diagnostic question in clinical settings.
Growth from Solutions
Growth from solutions is the crystallization of a compound whose chemical composition differs markedly from that of the initial liquid phase. Commonly used solvents are water, multicomponent aqueous or nonaqueous solutions, and melts of some chemical compounds. Differentiations are made based on growth temperatures and on the chemical nature of the solvent. In growth from low-temperature aqueous solutions, the temperatures generally do not exceed 80–90°C; in growth from superheated aqueous solutions (hydrothermal method), they reach 800°C, and in growth from salt melts (molten-salt, flux, or fluxed melt growth), they usually do not exceed 1200–1300°C, but sometimes reach 1500°C.