Pre-radiotherapy FDG PET predicts radiation pneumonitis in lung cancer

Background: A retrospective analysis is performed to determine if pre-treatment [¹⁸ F]-2-fluoro-2-deoxyglucose positron emission tomography/computed tomography (FDG PET/CT) image derived parameters can predict radiation pneumonitis (RP) clinical symptoms in lung cancer patients. Methods and Materials: We retrospectively studied 100 non-small cell lung cancer (NSCLC) patients who underwent FDG PET/CT imaging before initiation of radiotherapy (RT). Pneumonitis symptoms were evaluated using the Common Terminology Criteria for Adverse Events version 4.0 (CTCAEv4) from the consensus of 5 clinicians. Using the cumulative distribution of pre-treatment standard uptake values (SUV) within the lungs, the 80th to 95th percentile SUV values (SUV₈₀ to SUV₉₅) were determined. The effect of pre-RT FDG uptake, dose, patient and treatment characteristics on pulmonary toxicity was studied using multiple logistic regression. Results: The study subjects were treated with 3D conformal RT (n = 23), intensity modulated RT (n = 64), and proton therapy (n = 13). Multiple logistic regression analysis demonstrated that elevated pre-RT lung FDG uptake on staging FDG PET was related to development of RP symptoms after RT. A patient of average age and V₃₀ with SUV₉₅ = 1.5 was an estimated 6.9 times more likely to develop grade ≥ 2 radiation pneumonitis when compared to a patient with SUV₉₅ = 0.5 of the same age and identical V₃₀. Receiver operating characteristic curve analysis showed the area under the curve was 0.78 (95% CI = 0.69 - 0.87). The CT imaging and dosimetry parameters were found to be poor predictors of RP symptoms. Conclusions: The pretreatment pulmonary FDG uptake, as quantified by the SUV₉₅, predicted symptoms of RP in this study. Elevation in this pre-treatment biomarker identifies a patient group at high risk for post-treatment symptomatic RP.