Reproducibility of Intratumor Distribution of 18F-Fluoromisonidazole in Head and Neck Cancer

Abstract

Hypoxia is one of the main causes of the failure to achieve local control using radiotherapy. This is due to the increased radioresistance of hypoxic cells. (18)F-fluoromisonidazole ((18)F-FMISO) positron emission tomography (PET) is a noninvasive imaging technique that can assist in the identification of intratumor regions of hypoxia. The aim of this study was to evaluate the reproducibility of (18)F-FMISO intratumor distribution using two pretreatment PET scans. We enrolled 20 head and neck cancer patients in this study. Of these, 6 were excluded from the analysis for technical reasons. All patients underwent an (18)F-fluorodeoxyglucose study, followed by two (18)F-FMISO studies 3 days apart. The hypoxic volumes were delineated according to a tumor/blood ratio >or=1.2. The (18)F-FMISO tracer distributions from the two (18)F-FMISO studies were co-registered on a voxel-by-voxel basis using the computed tomography images from the PET/computed tomography examinations. A correlation between the (18)F-FMISO intensities of the corresponding spatial voxels was derived. A voxel-by-voxel analysis of the (18)F-FMISO distributions in the entire tumor volume showed a strong correlation in 71% of the patients. Restraining the correlation to putatively hypoxic zones reduced the number of patients exhibiting a strong correlation to 46%. Variability in spatial uptake can occur between repeat (18)F-FMISO PET scans in patients with head and neck cancer. Blood data for one patient was not available. Of 13 patients, 6 had well-correlated intratumor distributions of (18)F-FMISO-suggestive of chronic hypoxia. More work is required to identify the underlying causes of changes in intratumor distribution before single-time-point (18)F-FMISO PET images can be used as the basis of hypoxia-targeting intensity-modulated radiotherapy.