Detection of tumor response to radiation therapy by in vivo proton MR spectroscopy

Purpose: These studies were performed to investigate the effects of radiation on levels of metabolites such as lactate and choline compounds detected by ¹H magnetic resonance spectroscopy (MRS). The purpose was to determine the ability of spatially localized ¹H MRS to detect tumor response to radiation therapy. Methods and Materials: Proton spectroscopic images were obtained from RIF-1 tumors with voxel spatial resolutions of 8-16 mm³ before and at 24 and 48 h following 2, 4, and 20 Gy of γ-radiation. Results: Lactate levels decreased significantly for all doses by 48 h. Tumors irradiated with 2 and 4 Gy showed a significant decrease by 48 h, but not at 24 h. A group of sham-irradiated control animals demonstrated no significant changes in lactate over the period of observation. Conclusions: Changes in lactate observed in this study are consistent with an increased blond flow observed in previous studies (15) in the same tumor model following 20 Gy X- irradiation. These studies point to the feasibility of detecting response to clinical doses of fractionated radiation therapy by ¹H MRS.