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Sci-Fri PM: Delivery - 09: Response of a tumor xenograft model to radiation therapy using magnetic resonance spectroscopy.

9.4T 1 H magnetic resonance spectroscopy (MRS) was utilized to track the response of mouse xenograft glioblastoma multiform (GBM) brain tumors to single fraction radiation therapy. Six metabolites were analyzed with LCModel: alanine (Ala), myo-inositol (Ins), taurine (Tau), creatine and phosphocreatine (Cr + PCr), glutamine and glutamate (Glu + Gln), and total choline (glycerophosphocholine + phosphocholine) (GPC + PCh). 11 mice received 800 cGy of 200 kVp x-rays, 5 were untreated controls. PRESS spectra (27 μL volumes) were acquired at multiple time points for treated and control animals. In treated animals, all metabolite : water ratios decreased 3 days post-treatment, with further decreases at day 7, and then increases at day 14 relative to the 7 day mark. Concentrations on day 7 relative to pre-treatment were as follows: 0.42 (Ala), 0.43 (Ins), 0.68 (Tau), 0.52 (GPC+PCh), 0.49 (Cr + PCr) and 0.78 (Glu + Gln). Metabolite ratios did not correlate with tumor volume in control animals, suggesting a real therapeutic response was observed. Our 1 H MRS data suggests that perturbations in the metabolic signature of GBM cancers occur in response to irradiation. Such changes in the metabolite : water concentration ratios could potentially be exploited for the improvement of radiotherapy.