[Hypoxyradiotherapy: changes in the oxygen partial pressure distribution in the tumor and in the healthy tissue under acute respiratory hypoxia]

Abstract

Purpose: Based on the oxygen effect a new therapeutic modality has been developed to protect healthy tissues while breathing hypoxic gas mixture during irradiation.

Material and methods: The effect of breathing hypoxic gas mixture (8.1% O2) on pO2 in Yoshida sarcoma and muscle was studied using rats of Wistar strain. Different fractionation schedules were used: 10 x 3 Gy, 6 x 5 Gy and 3 x 10 Gy. Tissue oxygenation was assessed with a polarographic electrode system.

Results: The median pO2 in Yoshida sarcoma was 10 mm Hg. 21% of pO2-values were lower than 5 mm Hg. During breathing of hypoxic gas mixture no significant changes in median tumor pO2 or radiobiologic hypoxic values (< or = 5 mm Hg) were recorded. The median pO2 in muscle was 30 mm Hg. During breathing of gas hypoxic mixture a significant decrease of the median to the value 12 mm Hg and an increase of the radiobiologic hypoxic values (p < 0.00001) were observed. The changes of pO2-values were constant independent from fractionation.

Conclusions: Between tumor and healthy tissue exists a significant difference regarding changes in the radiobiologic fraction during breathing of hypoxic gas mixture. This fact explains the experimental and clinical experience, that the breathing hypoxic gas mixture protects the healthy tissue without changes in the radiosensibility of chronic hypoxic tumor tissue.