³¹P magnetic resonance spectroscopy for estimating the radiation response of a murine mammary tumor

Abstract

³¹P magnetic resonance spectroscopy (³¹P-MRS) can be used to asses the early response of tumors to treatment. The aim of this study was to investigate the radiation response of tumors in vivo and to correlate it with tumor growth. FM3A tumors were subcutaneously transplanted into the lower backs of C3H/He mice. Tumors were irradiated 7 days after transplantation receiving a single dose of 10Gy. In the sham irradiation control group, ³¹P-MRS showed that the β-ATP/Pi and PCr/Pi ratios decreased gradually as tumor size increased with time. In the radiation group, there was an initial rise and subsequent decrease of the β-ATP/Pi and PCr/Pi ratios. The maximum β-ATP/Pi ratio was observed on day 5 after irradiation. In the tumor growth delay assay using a single dose of 10Gy, the tumor did not grow up to day 11. The peak values of the β-ATP/Pi and PCr/Pi ratios after irradiation were observed before changes in tumor volume occurred. Our results suggested that changes in metabolites observed by ³¹P-MRS could be a useful indicator for monitoring the effects of radiation therapy, such as reoxygenation and regrowth.