Studies on Tumor Oxygenation in a Rat Rhabdomyo-Sarcoma during Fractionated Irradiation
The oxygenation status of a tumor is certainly one of the major factors which influences the response of a tumor to radiotherapy (7, 9, 16, 22). Due to a chaotic and temporarily fluctuating tumor blood perfusion (5, 24, 25) oxygenation of tumor tissue is inadequate, and consequently, most experimental and human tumors contain varying proportions of hypoxic tumor cells (11, 18, 19, 25) which are radioresistant. It is supposed that these cells limit the curability of some types of tumors by radiotherapy. There is some experimental evidence that after irradiation with either single or fractionated doses of X-rays, a proportion of surviving cells which were initially hypoxic becomes reoxygenated, thereby changing the oxygenation status of the tumor (1, 14, 21, 23). However, most studies on reoxygenation have been carried out in experimental tumors using the paired survival curve assay (18) and doses up to about 30 Gy. Grau and Overgaard (8) reported on the reoxygenation of an irradiated mouse mammary carcinoma using the clamped local tumor control assay. After a priming dose of 20 Gy reoxygenation occurred completely. However, after a priming dose of 40 Gy only a transient reoxygenation was observed, followed by an increase of the hypoxic fraction slightly above the oxygenation level of untreated tumors. Since there is only limited knowledge about the changes in tumor oxygenation during radiotherapy (2, 4, 6), it was the aim of this study to determine systematically the oxygenation status of a rat tumor in vivo in the course of a fractionated irradiation.
KeywordsMean Arterial Blood Pressure Oxygenation Status Priming Dose Tumor Blood Flow Respiratory Volume
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