Prospective evaluation of pretreatment and intratreatment FDG PET‐CT SUV stability in primary head and neck cancer

Purpose To evaluate standardized uptake value (SUV) stability on pretreatment and intratreatment 18‐fluorodeoxyglucose (FDG) positron emission tomography‐computed tomography (PET‐CT) in patients undergoing definitive CRT for head and neck cancer (HNC). Methods Primary tumor and nodal volumes of interest (VOIs) from HNC patients were contoured on the pretreatment and intratreatment PET‐CT by two independent observers. SUV stability was measured with intersection calculations (DICE, overlap fraction, center to center) between the VOIs at threshold levels of 50%, 60%, 70%, 80%, and 90% of the SUV maximum. Results The mean calculated DICE of the 50%, 60%, 70%, 80%, 90% SUV threshold was 0.53, 0.48, 0.41, 0.28, and 0.12, respectively. The mean calculated overlap fraction was 0.71, 0.65, 0.58, 0.43, and 0.2, respectively. Center‐center difference demonstrates spatial variability of 7.8, 8.2, 8.6, 9.5, and 11.2 mm for these SUV subvolumes of interest. Conclusions HNC subvolumes defined by SUV thresholding technique in FDG PET‐CT imaging do not remain physically stable during (chemo)RT. Highlights All pretreatment and intratreatment SUV thresholds (50%‐90%) overlap indexes are low during the course of (chemo)radiation. Pretreatment and intratreatment center to center variation further corroborates that all FDG threshold volumes do not remain stable during treatment. No difference in SUV threshold stability was seen between p16 positive and negative tumors.