LAUSR

The high rates of failure in the radiotherapy target volume suggest that patients with stage II or III non-small-cell lung cancer (NSCLC) should receive an increased total dose of radiotherapy. 2-Deoxy-2-[18F]fluoro-d-glucose ([18F]FDG) and [18F]fluoromisonidazole ([18F]FMISO) (hypoxia) uptake on pre-radiotherapy positron emission tomography (PET)/X-ray computed tomography (CT) have been independently reported to identify intratumor subvolumes at higher risk of relapse after radiotherapy. We have compared the [18F]FDG and [18F]FMISO volumes defined by PET/CT in NSCLC patients included in a prospective study. Thirty-four patients with non-resectable lung cancer underwent [18F]FDG and [18F]FMISO PET/CT before (pre-RT) and during radiotherapy (around 42 Gy, per-RT). The criteria were to delineate 40 % and 90 % SUVmax thresholds on [18F]FDG PET/CT (metabolic volumes), and SUV > 1.4 on pre-RT [18F]FMISO PET/CT (hypoxic volume). The functional volumes were delineated within the tumor volume as defined on co-registered CTs. The mean pre-RT and per-RT [18F]FDG volumes were not statistically different (30.4 cc vs 22.2; P = 0.12). The mean pre-RT SUVmax [18F]FDG was higher than per-RT SUVmax (12.7 vs 6.5; P < 0.0001). The mean [18F]FMISO SUVmax and volumes were 2.7 and 1.37 cc, respectively. Volume-based analysis showed good overlap between [18F]FDG and [18F]FMISO for all methods of segmentation but a poor correlation for Jaccard or Dice Indices (DI). The DI maximum was 0.45 for a threshold at 40 or 50 %. The correlation between [18F]FDG and [18F]FMISO uptake is low in NSCLC, making it possible to envisage different management strategies as the studies in progress show.