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-HTV) derived from FMISO-PET images acquired before and during radiochemotherapy and to uncover correlations between extent and severity of hypoxia and treatment outcome.

Material And Methods: 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 maps and corresponding pO-HTVs (pO-HTV, pO-HTV, pO-HTV) were contoured at 10 mmHg. Different parameters describing the pO-HTV time evolution were considered, such as the percent and absolute difference between the pO-HTVs (%HTV and HTV-HTV with i,j = 1, 2, 3, respectively) and the slope of the linear regression curve fitting the pO-HTVs in time. Correlations were sought between the pO-HTV evolution parameters and loco-regional recurrence (LRR) using the Receiver Operating Characteristic method.

Results: The Area Under the Curve values for %HTV, HTV-HTV, HTV-HTV and the slope of the pO-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-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.