Evolution of the hypoxic compartment on sequential oxygen partial pressure maps during radiochemotherapy in advanced head and neck cancer

BACKGROUND AND PURPOSE: Longitudinal Positron Emission Tomography (PET) with hypoxia-specific radiotracers allows monitoring the time evolution of regions of increased radioresistance and may become fundamental in determining the radiochemotherapy outcome in Head-and-Neck Squamous Cell Carcinoma (HNSCC). The aim of this study was to investigate the evolution of the hypoxic target volume on oxygen partial pressure maps (pO(2)-HTV) derived from (18)FMISO-PET images acquired before and during radiochemotherapy and to uncover correlations between extent and severity of hypoxia and treatment outcome. MATERIAL AND METHODS: (18)FMISO-PET/CT images were acquired at three time points (before treatment start, in weeks two and five) for twenty-eight HNSCC patients treated with radiochemotherapy. The images were converted into pO(2) maps and corresponding pO(2)-HTVs (pO(2)-HTV(1), pO(2)-HTV(2), pO(2)-HTV(3)) were contoured at 10 mmHg. Different parameters describing the pO(2)-HTV time evolution were considered, such as the percent and absolute difference between the pO(2)-HTVs (%HTV(i,j) and HTV(i)-HTV(j) with i,j = 1, 2, 3, respectively) and the slope of the linear regression curve fitting the pO(2)-HTVs in time. Correlations were sought between the pO(2)-HTV evolution parameters and loco-regional recurrence (LRR) using the Receiver Operating Characteristic method. RESULTS: The Area Under the Curve values for %HTV(1,2), HTV(1)-HTV(2), HTV(1)-HTV(3) and the slope of the pO(2)-HTV linear regression curve were 0.75 (p = 0.04), 0.73 (p = 0.02), 0.73 (p = 0.02) and 0.75 (p = 0.007), respectively. Other parameter combinations were not statistically significant. CONCLUSIONS: The pO(2)-HTV evolution during radiochemotherapy showed predictive value for LRR. The changes in the tumour hypoxia during the first two treatment weeks may be used for adaptive personalized treatment approaches.