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 (SUV(80) to SUV(95) 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 V(30) with SUV(95)=1.5 was an estimated 6.9 times more likely to develop grade ≥ 2 radiation pneumonitis when compared to a patient with SUV(95)=0.5 of the same age and identical V(30). 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 SUV(95), 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.