Integrating (18)F‐FDG PET/CT with lung dose‐volume for assessing lung inflammatory changes after arc‐based radiotherapy for esophageal cancer: A pilot study

OBJECTIVE: The incidence of radiation pneumonitis (RP) has a highly linear relationship with low‐dose lung volume. We previously established a volume‐based algorithm (VBA) method to improve low‐dose lung volume in radiotherapy (RT). This study assessed lung inflammatory changes by integrating fluorine‐18‐fluorodeoxyglucose positron emission tomography/computed tomography ((18)F‐FDG PET/CT) with VBA for esophageal cancer patients undergoing arc‐based RT. METHODS: Thirty esophageal cancer patients received (18)F‐FDG PET/CT imaging pre‐RT and post‐RT were included in a retrospective pilot study. We fused lung doses and parameters of PET/CT in RT planning. Based on VBA, we used the 5Gy isodose curve to define high‐dose (HD) and low‐dose (LD) regions in the lung volume. We divided patients into non‐RP (nRP) and RP groups. The maximum, mean standardized uptake value (SUVmax, SUVmean), global lung glycolysis (GLG), mean lung dose (MLD) and V(5–30) in lungs were analyzed. Area under the curve values were utilized to identify optimal cut‐off values for RP. RESULTS: Eleven patients in the nRP group and 19 patients in the RP group were identified. In 30 RP lungs, post‐RT SUVmax, SUVmean and GLG of HD regions showed significant increases compared to values for pre‐RT lungs. There were no significant differences in values of 22 nRP lungs. Post‐RT SUVmax and SUVmean of HD regions, MLD, and lung V(5) and V(10) in RP lungs were significantly higher than in nRP lungs. For detecting RP, the optimal cut‐off values were post‐RT SUVmax > 2.28 and lung V(5) > 47.14%. CONCLUSION: This study successfully integrated (18)F‐FDG PET/CT with VBA to assess RP in esophageal cancer patients undergoing RT. Post‐RT SUVmax > 2.28 and lung V(5) > 47.14% might be potential indicators of RP.