A pilot study comparing intratumoral oxygenation using the comet assay following 2.5% and 5% carbogen and 100% oxygen

Purpose: Tumor hypoxia has been purported to be an important biologic facto r in the failure of radical radiotherapy to achieve local control in many t umor types. This study was designed to evaluate the effect of breathing hig h oxygen content gas mixtures (oxygen with 0%, 2.5%, or 5% carbon dioxide) on tumor oxygenation measured using the Eppendorf polarographic oxygen elec trode and the comet assay in accessible, hypoxic human tumors. Methods and Materials: Using Eppendorf pO(2) histography to identify hypoxi c tumors (median pO(2) less than or equal to 10 mmHg), eligible patients we re systematically allocated either 100% oxygen (O-2) or oxygen with 2.5% or 5% carbon dioxide (CO,), Tumors were treated with 6-10 Gy during which two fine needle aspirates (FNA) were obtained from different regions of the le sion, one at midway and the other at completion of the radiation exposure. Gas breathing was initiated 4 min before radiation was commenced. A 10-min interval was specified between the first and second halves of the radiation exposure to allow near maximal DNA repair prior to the second half of the radiation treatment. FNAs were performed within 2 min of cessation of radia tion and the cells immediately suspended in buffered saline at 4 degreesC f or analyses of hypoxic fraction using the comet assay. Results: Fifteen evaluations were performed in 13 patients with hypoxic tum ors (median O-2 tension 2.75 mmHg) treated with a median dose of 8 Gy, The median hypoxic fraction determined using the comet assay fell from 0.36 to 0.13 (p = 0.001, Wilcoxon signed rank test) due to the addition of high oxy gen content gases. Conclusions: In tumors defined as hypoxic using Eppendorf pO(2) histography , a statistically significant reduction in the hypoxic fraction with the co met assay was found following administration of high oxygen content gases. These preliminary findings reveal a trend suggesting that 5% carbogen may r educe the hypoxic fraction by a greater margin than either 100% oxygen or 2 .5% carbogen, (C) 2001 Elsevier Science Inc.