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

Abstract

Purpose-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.Methods and Materials-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 Ffluorodeoxyglucose study, followed by two 18 F-FMISO studies 3 days apart. The hypoxic volumes were delineated according to a tumor/blood ratio ≥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.Results-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%.Conclusion-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 singletime-point 18 F-FMISO PET images can be used as the basis of hypoxia-targeting intensity-modulated radiotherapy.

Cycling hypoxia and free radicals regulate angiogenesis and radiotherapy response

“…These results suggest that vascular remodelling might be responsible for the slower frequency of cycling hypoxia. Recent 18 Fmisonidazole (a hypoxia marker drug) positron-emission tomography (PET) studies in human patients with head and neck cancer have verified that large regions of tumours can experience the slower frequency cycling hypoxia 98 . In these studies, serial PET studies scheduled 3 days apart showed that hypoxic tumour zones moved or changed in size between sequential studies.…”

Resolution in PET hypoxia imaging: Voxel size matters

“…A particular concern is the time delay between scans and initiation of treatment. Nehmeh and colleagues [30] examined the regional spatial repeatability of FMISO hypoxia scans by performing two scans 3 days apart, followed by a voxel-by-voxel comparison of the two scans. Interestingly, although many patients showed reasonable scan-to-scan correlation nearly half of the patients were characterized by a poor geographical match between the two scans, which may severely, reduce the efficacy of hypoxia-targeting intensity modulated radiotherapy [31].…”

Dynamic contrast enhanced magnetic resonance imaging of bladder cancer and implications for biological image-adapted radiotherapy

“…High spatial resolution of the intensity modulated beams is needed to provide the irregular dose distributions required. It may also be relevant to evaluate the temporal evolution of image parameters during the course of treatment [9,21], as this may have an impact on the dose prescription map. The situation is further complicated by the considerable geometrical uncertainties taking place during RT (bladder/tumor motion) for the present patient group [22].…”