31P-MRS study for the assessment of tumor response after radiotherapy and/or hyperthermia

The metabolic changes of human lung cancer implanted in nude mice were studied by the use of in vivo 31P nuclear magnetic resonance spectroscopy (31P-MRS) after radiotherapy, hyperthermia or the combined therapy of radiation and hyperthermia. 31P-MRS of the tumors showed increased Pi/β-NTP ratio and acidic pH value on 1 day after hyperthermia, that indicated metabolic decline caused by hyperthermia. On the other hand, lower Pi/β-NTP ratios during 3 to 10 days after irradiation suggested metabolic activation of the tumors. In the tumors treated with the combined therapy, 31P-MRS revealed increase of Pi/β-NTP ratio within 1 day and its decrease subsequent 6 to 10 days after treatment, that indicated additive bi-phasic changes induced by radiation and hyperthermia, respectively. Since Pi/β-NTP ratio had significant correlation to the tumor blood perfusion measured by hydrogen gas clearance studies, these bi-phasic changes were considered to correspond to two different physiological states, namely, ischemic and reperfused states. 31P-MRS obtained from tumors could be useful to asses the physiological consequence following radiation, hyperthermia or the combined therapy. (author)