Tissue oxygenation in a murine SCC VII tumor after X-ray irradiation as determined by EPR spectroscopy

PurposeThe goal of this study was to clarify the dynamics of oxygenation (partial pressure of oxygen, pO2) in SCC VII murine tumors in mice after X-ray irradiation.Materials and methodsChanges in pO2 in tumors were measured by 1.2-GHz electron paramagnetic resonance (EPR) spectroscopy after they were exposed to various doses of irradiation. The pO2 in tumors was followed for up to six days after irradiation at doses of 0, 5, 10, 15, and 20 Gy. Paramagnetic crystals were used as an oximetry probe and implanted into normal or tumor tissues in mice for prolonged periods.ResultsThe pattern of tumor oxygen after a single dose of radiation with the 5-Gy dose was different from those with other doses (10, 15, and 20 Gy). After 5 Gy, pO2 increased rapidly (P < 0.01, Student’s t test) and then returned to the level observed before irradiation by 12 h (P < 0.01). In contrast, after 10, 15, or 20 Gy, pO2 increased rapidly by 6 h after irradiation, continued to increase until at least 24 h (P < 0.01), and then gradually decreased.ConclusionsIn tumors that received 5 Gy, post-irradiation increases in pO2 at 4 h after irradiation were detected by EPR oximetry (P < 0.01) noninvasively.