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

Abstract

Introduction. Polarographic oxygen-sensitive electrodes have demonstrated prognostic significance of hypoxia. However, its routine application is limited. ¹⁸F-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 pO₂ 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, ¹⁸FDG-PET or by clinical examination. The oxygenation status of the tumors was assessed using ¹⁸F-FMISO PET imaging followed by Eppendorf pO₂ electrode measurements. Data were compared in a ‘virtual voxel’, resulting in individual histograms from each tumor. Results. The percentages of pO₂ ≤ 5 mmHg ranged from 9 to 94% (median 43%) for all 18 tumors. For ¹⁸F-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 ¹⁸F-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 ¹⁸F-FMISO PET and Eppendorf pO₂ 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 pO₂ measurements as compared to ¹⁸F-FMISO PET.