[18 F]fluorodeoxyglucose Uptake Patterns in Lung Before Radiotherapy Identify Areas More Susceptible to Radiation-Induced Lung Toxicity in Non-Small-Cell Lung Cancer Patients

Purpose Our hypothesis was that pretreatment inflammation in the lung makes pulmonary tissue more susceptible to radiation damage. The relationship between pretreatment [18 F]fluorodeoxyglucose ([18 F]FDG) uptake in the lungs (as a surrogate for inflammation) and the delivered radiation dose and radiation-induced lung toxicity (RILT) was investigated. Methods and Materials We retrospectively studied a prospectively obtained cohort of 101 non-small-cell lung cancer patients treated with (chemo)radiation therapy (RT). [18 F]FDG-positron emission tomography-computed tomography (PET-CT) scans used for treatment planning were studied. Different parameters were used to describe [18 F]FDG uptake patterns in the lungs, excluding clinical target volumes, and the interaction with radiation dose. An increase in the dyspnea grade of 1 (Common Terminology Criteria for Adverse Events version 3.0) or more points compared to the pre-RT score was used as an endpoint for analysis of RILT. The effect of [18 F]FDG and CT-based variables, dose, and other patient or treatment characteristics that effected RILT was studied using logistic regression. Results Increased lung density and pretreatment [18 F]FDG uptake were related to RILT after RT with univariable logistic regression. The 95th percentile of the [18 F]FDG uptake in the lungs remained significant in multivariable logistic regression ( p = 0.016; odds ratio [OR] = 4.3), together with age ( p = 0.029; OR = 1.06), and a pre-RT dyspnea score of ≥1 ( p = 0.005; OR = 0.20). Significant interaction effects were demonstrated among the 80th, 90th, and 95th percentiles and the relative lung volume receiving more than 2 and 5 Gy. Conclusions The risk of RILT increased with the 95th percentile of the [18 F]FDG uptake in the lungs, excluding clinical tumor volume (OR = 4.3). The effect became more pronounced as the fraction of the 5%, 10%, and 20% highest standardized uptake value voxels that received more than 2 Gy to 5 Gy increased. Therefore, the risk of RILT may be decreased by applying sophisticated radiotherapy techniques to avoid areas in the lung with high [18 F]FDG uptake.