Identifying hypoxia in human tumors: A correlation study between 18F-FMISO PET and the Eppendorf oxygen-sensitive electrode

Introduction. Polarographic oxygen-sensitive electrodes have demonstrated prognostic significance of hypoxia. However, its routine application is limited. F-18-FMISO PET scans are a noninvasive approach, able to measure spatial and temporal changes in hypoxia. The aim of this study was to examine the association between measures of hypoxia defined by functional imaging and Eppendorf pO(2) electrodes. Materials and methods. A total of 18 patients were included, nine squamous cell carcinoma of the head and neck and nine soft tissue tumors. The tumor volume was defined by CT, MRI, (18)FDG-PET or by clinical examination. The oxygenation status of the tumors was assessed using F-18-FMISO PET imaging followed by Eppendorf pO(2) electrode measurements. Data were compared in a 'virtual voxel', resulting in individual histograms from each tumor. Results. The percentages of pO(2) <= 5 mmHg ranged from 9 to 94% (median 43%) for all 18 tumors. For F-18-FMISO PET the T/M ratio ranged from 0.70 to 2.38 (median 1.13). Analyzing the virtual voxel histograms tumors could be categorized in three groups: Well oxygenated tumors with no hypoxia and concordance between the F-18-FMISO data and the Eppendorf measurements, hypoxic tumors likewise with concordance between the two assays and inconclusive tumors with no concordance between the assays. Conclusion. This study analyzed the relationship between F-18-FMISO PET and Eppendorf pO(2) electrode measurements by use of a virtual voxel model. There was a spectrum of hypoxia among tumors that can be detected by both assays. However no correlation was observed, and in general tumors were more hypoxic based on Eppendorf pO(2) measurements as compared to F-18-FMISO PET.