In Vivo Assessment of Hypoxia in Gastro-intestinal Cancer Using 18F-HX4-PET: an Optimization and Reproducibility Study

Several studies have shown that tumour hypoxia may have a negative impact on the outcome of anticancer treatment. Assessment of tumor hypoxia at baseline or shortly after start of treatment may serve as a predictive marker to determine treatment efficacy at an early stage. Preferably, such an assessment is performed in vivo and non-invasively.Non-invasive imaging with positron emission tomography (PET) using the 2-nitroimidazole nucleoside analogue, 3-18F-fluoro-2-(4-((2-nitro-1H-imidazol-1-yl)methyl)-1H-1,2,3-triazol-1- yl)propan-1-ol (18F-HX4), was tested as a new marker of tumor hypoxia. Before hypoxia-measurements can be clinically implemented for response prediction, the reproducibility of the technique should be assessed for each specific tumor type. Knowledge of reproducibility is needed to determine what change in parameters between two examinations can be considered relevant in an individual patient. Assessment of reproducibility becomes even more important in early response monitoring since the changes in the tumor induced by the treatment may be smaller during the treatment compared to response monitoring after completion of treatment. Also, as image quality of 18F-HX4-PET increases with increasing time intervals after injection, determination of the optimal time point for measurement of hypoxia is warranted.