Prognostic Evaluation of 18fmiso Pet-ct in Head and Neck Cancer

Cancer of Head and Neck, Head and Neck Neoplasms

Head and neck neoplasms, Positron Emission Tomography, F18 fluoromisonidazole

Head and neck cancer is the sixth most frequent cancer worldwide, excluding lymphomas and skin cancer. If 18FDG PET is considered today as a standard tool in patients with head and neck squamous cell carcinoma (HNSCC) not only for tumoral or nodal staging but also for assessment of distant metastases and synchronous second primary malignancies, hypoxia is one of the most important prognostic factors in radiotherapy of this type of tumors. The only gold standard method for direct determination of oxygen tension is based on using oxygen electrodes showing a good relation with clinical outcome but complex in its realisation. So, PET using 18F-FMISO has been described to be useful for the non invasive assessment of hypoxia in cancer. Especially in France, the use of this radiotracer is very limited and there is no standardised methodology to acquire and quantify 18F-FMISO signal. So there is a need for a rigorous evaluation of this PET tracer. In another way, it could be a very useful tool for evaluation of new therapies and modification of volumes in radiotherapy.

Hypoxia is one of the major worst prognostic factors of clinical outcome in cancer. It is actually admitted that hypoxia is heterogeneous, variable within different tumour types and that it varies spatially and temporally in a tumor. Hypoxia induce proteomic and gene expression changes that lead to increase angiogenesis, invasion and metastases. So, the hypoxic fraction in solid tumours reduces their sensitivity to conventional treatment modalities, modulating therapeutic response to ionizing radiation or certain chemotherapeutic agents. This is particularly important in head and neck cancers (HNC). Hypoxic cells in solid tumours could influence local failure following radiotherapy and has been associated with malignant progression, loco regional spread and distant metastases and represents an increasing probability of recurrence. Thus, the non-invasive determination and monitoring of the oxygenation status could be of tumours is of importance to predict patient outcome and eventually modify therapeutic strategies in those tumours. Today, the oxygenation status of individual tumours is not assessed routinely. Numerous different approaches have been proposed to identify hypoxia in tumours. Eppendorf oxygen electrode measurements (pO2 histography) may be considered as a 'gold standard' for hypoxia in human malignancies. However, it is an invasive method being confined to superficial, well accessible tumours and requires many measures. PET using \[18F\]Fluoro-deoxyglucose (18F-FDG), allows non-invasive imaging of glucose metabolism and takes a growing place in cancer staging, But 18F-FDG can't assess correctly the oxygenation status of tumours. PET with appropriate radiotracers enables non-invasive assessment of presence and distribution of hypoxia in tumours. Nitroimidazoles are a class of electron affinic molecules that were shown to accumulate in hypoxic cells in vitro and in vivo. \[18F\]-FMISO is the most frequently used tracer ; its intracellular retention is dependent on oxygen tension. Consequently, \[18F\]-FMISO has been used as a non-invasive technique for detection of hypoxia in humans. Different authors have demonstrated that it is suitable to localize and quantify hypoxia. Thus, \[18F\]-FMISO PET has been studied to evaluate prognosis and predict treatment response. However, some investigators report an unclear correlation between Eppendorf measurements and standardized uptake values (SUV). This observation may be explained by the structural complexity of hypoxic tumour tissues. Nevertheless, there is a need of standardized procedures to acquire and quantify \[18F\]-FMISO uptake. Today, the use of this tracer is very limited in clinic and the academic studies have included small populations of patients and suffer of the heterogeneity of technical procedures. The aim of this study is to determine the optimal acquisition protocol and image reconstruction to describe \[18F\]-FMISO uptake in HNC, then, to validate \[18F\]-FMISO-PET as a predictive marker of response to treatment.

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