RELATIONSHIP BETWEEN RADIOBIOLOGICAL HYPOXIA IN TUMORS AND ELECTRODE MEASUREMENTS OP TUMOR OXYGENATION

Purpose: To determine whether electrode measurements of tumor oxygenat ion, made in a variety of murine tumor models, correlate with estimate s of radiobioiogical hypoxia in the same tumor systems. Methods and Ma terials: The tumor models used were a C3H mammary carcinoma grown in t he feet of CDF1 mice; the SCCVII, KHT and RIF-1 tumors grown in the fe et or flanks of C3H/Km mice; and the CaNT and SaF tumors grown on the backs of CBA mice. All treatments were performed when tumors were abou t 200 mm(3) in size. Radiobiological hypoxic fractions were determined using either a paired survival curve assay, with survival measured 0- 24 h after irradiation, or using a clamped tumor control assay, with p ercent local tumor control estimated 90 days after treatment. Measurem ents of tumor oxygen partial pressure (pO(2)) distributions were perfo rmed using Eppendorf oxygen electrodes. Results: The hypoxic fractions determined from the radiation response data were about 1% in RIF-1 an d SCCVII, 12% in C3H and KHT, 28% in CaNT and up to 38% in SaF tumors. When this data was compared with the tumor oxygenation measurements i t was found that as hypoxic fraction increased the mean, median, and t he percentage of pO(2) values less than or equal to 5 mmHg showed a tr end towards poorer oxygenation status. However, none of these pO(2) ch anges were significantly correlated with hypoxia. Moreover, the pO(2) values less than or equal to 2.5 mmHg indicated an improvement in oxyg en status with increasing hypoxic fraction. Conclusion: Electrode meas urements of tumor oxygenation alone may, therefore, not be a good indi cator of tumor hypoxia across different tumor cell lines.