Abstract:

Objective   To observe the 1H-MRS of C6 glioma models before and after radiotherapy, and to discuss its effect in detecting early response in oncotherapy. Methods   C6 glioma models of SD rats(treated group, n=10； untreated group, n=12)were applied and a single dose of 15Gy was given to the treated group 9 days after tumor implantation. After tumor implantation, 1H-MRS was used to detect changes in tumor metabolism, such as N-Acetyl-L-aspartic acid (NAA), Choline (Cho) and Lactic acid (Lac). MRI was used to detect changes of tumor volume. Changes of metabolism and volume in the two groups were observed and correlation analysis was done for indices changes and tumor size changes of the two groups. Results   Rate of tumor formation was 100% in all rats. In the untreated group (n=12), Cho and Lac showed an ascendant trend and NAA gradually decreased with tumor growth. Changes of tumor metabolites and tumor volume had significant correlations (Cho: r=0.958, P＜0.001；Lac: r=0.989, P＜0.001；NAA: r=－0.943, P＜0.001). In the treated group(n=10), Cho decreased from 3.37mmol/kg to 2.0mmol/kg(P＜0.01) 1 day after radiation, Lac decreased from 2.34mmol/kg to 1.59mmol/kg(P＜0.01) 3 days after radiation and there was no significant change in NAA(P＞0.05). Tumor volume increased 31.4%(P＜0.01) at 3rd day and began to shrink at 5th day after radiation, and then tumor growth inhibition appeared , the metabolic indices continued to fall and there was a correlation trend between tumor volume changes and metabolic indices (Cho: r=0.696, P=0.304; Lac: r=0.911, P＜0.089；NAA: r=－0.583, P＜0.417). Before volume changes detected by MRI began, inhibitive changes in metabolites detected by 1H-MRS had already happened. Conclusion   1H-MRS can detect metabolism changes of glioma such as NAA, Cho and Lac before and after noninvasive radiotherapy. It is more sensitive in monitoring early response to radiation than MRI and is an effective method in determining the short-term effect of treatments.

Key words: C6 glioma model; 1H -MRS; Radiotherapy; SD rats