Dynamics of tumor hypoxia assessed by 18F-FAZA PET/CT in head and neck and lung cancer patients during chemoradiation: possible implications for radiotherapy treatment planning strategies.

INTRODUCTION To define the optimal time point for the integration of hypoxia (18)F-FAZA-PET/CT information into radiotherapy treatment planning to benefit from hypoxia modification or dose escalation treatment. Therefore, we performed a prospective cohort study, using serial hypoxic imaging ((18)F-FAZA-PET/CT) prior to and at several time-points during (chemo)radiotherapy (CHRT) in six head and neck squamous cell (HNSCC) and six non-small cell lung cancer (NSCLC) patients. METHODS The spatio-temporal dynamics of tumor hypoxia and fractional hypoxic volumes (FHV) were evaluated using a voxel-by-voxel analysis based on a (18)F-FAZA-T/B ratio of 1.4 at four time points in HNSCC patients, at baseline (FAZA-BL), at week one (FAZA-W1), two (FAZA-W2), and four (FAZA-W4) during CHRT and at three time points in NSCLC patients (baseline; W2, W4). RESULTS Ten out of twelve patients showed a substantial pre-treatment tumor hypoxia representing a FHV⩾1.4 assessed by (18)F-FAZA-PET/CT. The median FHV was 38% (FAZA-BL), 15% (FAZA-W1), 17% (FAZA-W2) and 1.5% (FAZA-W4) in HNSCC patients, and 34% (FAZA-BL), 26% (FAZA-W2) and 26% (FAZA-W4) in NSCLC patients, respectively. Stable tumor hypoxia was observed in three HNSCC patients and two NSCLC patients at FAZA-W2. In three HNSCC patients and two NSCLC patients FHVs declined to non-detectable hypoxia levels at FAZA-W4 during CHRT, while two NSCLC patients, showed increasing FHVs. CONCLUSION Our results indicate that, instead of using the FAZA-BL scan as the basis for the dose escalation, FAZA-W2 of CHRT is most suitable and might provide a more reliable basis for the integration of (18)F-FAZA-PET/CT information into radiotherapy treatment planning for hypoxia-directed dose escalation strategies.