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

9.4T 1H 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 1H 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.