CHANGES IN P-31 NUCLEAR-MAGNETIC-RESONANCE WITH TUMOR-GROWTH IN RADIORESISTANT AND RADIOSENSITIVE TUMORS

In vivo 31P nuclear magnetic resonance (31P NMR) spectroscopy has been used to compare metabolic profile with tumor radiosensitivity. A radioresistant mammary carcinoma (MCa) and a radiosensitive methylcholanthrene-induced fibrosarcoma (Meth-A) were studied by 31P NMR spectroscopy in the tumor volume range of approximately 100-1200 mm3. The MCa showed a constant pH in this volume range; the ratio of phosphocreatine to inorganic phosphate (PCr/P(i)) for 160-300 mm3 tumors was 0.33 ± 0.11 (mean ± standard deviation) and did not change (0.29 ± .09) for tumors in the volume range of 600-1200 mm3. In comparison, the Meth-A showed a decrease in tumor pH as volume increased from 160-300 mm3 (pH 7.16 ± .04) to 600-1200 mm3 (pH 6.94 ± .07). Tumor PCr/P(i) decreased from 0.70 ± .16 (160-300 mm3) to 0.33 ± .16 (600-1200 mm3). The radiation doses for control of MCa-induced tumors in 50% of the treated tumors ranged from 65 (150-250 mm3) to 71 Gy (1000-1300 mm3) and for the Meth-A-induced tumors ranged from 35 (150-250 mm3) to 38 Gy (1000-1300 mm3). These results sugest that 31P NMR spectra may be a qualitative predictor of tumor hypoxia, although further studies of human and rodent tumors are necessary to support this hypothesis.