Heterogeneity of polarographic oxygen tension measurements in cervix cancer: An evaluation of within and between tumor variability, probe position, and track depth

PURPOSE: To evaluate the heterogeneity of cervix cancer oxygenation as measured using the Eppendorf polarographic electrode and define the optimal number of measurements required to adequately sample a cervix cancer. METHODS AND MATERIALS: Two to 6 tracks with 20-30 measurements per track were obtained in each of the 44 patients evaluated. One hundred sixty-eight tracks and 4719 measurements formed the basis of this analysis. Median pO2 and hypoxic proportion (HP5), defined as the percentage of pO2 values <5 mmHg, were calculated for each track and for each tumor. Within-tumor (W) and between-tumor (B) variability in oxygenation was evaluated using a variance component analysis. The standard error of the measured HP5 with each additional track in each patient was analysed as a function of the total number of tracks. RESULTS: The ratio W/W + B was 0.67 and 0.76 for median pO2 and HP5, respectively, indicating that multiple measurements are needed to adequately sample a tumor. The median value of the standard error of the HP5 decreased from 7.0 to 4.0% from the first to the fifth track, respectively. It was estimated that adding the sixth track would only result in a small change (<0.3%) in the standard error. There was no significant difference in oxygen tension measurements as a function of the location of the measurements around the circumference of the cervix or the depth along the measurement tracks. CONCLUSIONS: There is significant within tumor variability in oxygen tension in cervix cancer. Five tracks with 20-30 measurements per track is optimal to sample the oxygenation status of a cervix cancer. The present data does not suggest that there is a significant difference related to the position in the tumor at which the pO2 measurements were taken.