Distributions of pO2 values in various normal human tissues have been described in detail (49-53). The normal tissues were subcutaneous tissues surrounding tumors for ear, nose, and throat (ENT), sarcoma, and melanoma patients, normal brain for gliomas, and vaginal mucosa for cervix tumors (49-55). As expected, there is a scattering of the individual pO2 values in normal tissues between 1 mmHg and values typical for arterial blood (80-100 mmHg). Whatever the normal tissue, median pO2 ranged from 15 to 70 mmHg. For example, in patients with head and neck tumors, median pO2was 52 mmHg in the Institut Gustave-Roussy (IGR) experience (mean 54 mmHg) (52) and mean pO2 was 57 mmHg at Stanford (55).
The results obtained with the KIMOC 6650 have demonstrated that normal tissues are in general better oxygenated than solid tumors. This finding probably reflects the better vascularization of normal tissues than tumors, and the higher interstitial pressure present in tumors. In most studies, more than 90% of the values recorded in normal tissues were above 10 mmHg. At this oxygen tension, the relative radiosensitivity is close to a maximum, and only a small increase in sensitivity can be expected with an increase in oxygen delivery.
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