Intratreatment Fdg-Pet Imaging To Predict Radiation Induced Esophagitis During Chemoradiation Therapy For Esophageal Cancer

In this analysis we evaluated if changes in esophageal metabolic uptake on intra-treatment fluorodeoxyglucose positron emission tomography (FDG-PET) during chemoradiotherapy (CRT) for esophageal cancer correlates with the development of clinically significant radiation (RT)-induced esophagitis. From 2012 to 2016, 60 patients with esophageal cancer were prospectively enrolled and underwent PET/CT scans before therapy and after 30-36 Gy. All patients received carboplatin/paclitaxel-based CRT. Maximum esophagitis grade was recorded using the RTOG/EORTC scale. To determine the change in esophageal metabolic activity during CRT an esophageal region of interest (ROI) was contoured at the same esophageal location on the pre-treatment and intra-treatment PET/CT scans. The esophageal ROI consisted of 9 contiguous slices of the esophagus within the radiation field but separate from the hypermetabolic primary tumor. Rigid registration with manual edits for anatomical changes was performed to ensure the ROI was contoured at the same esophageal location on the pre-treatment and intra-treatment PET/CT scans. The relative change in peak standard uptake value (SUVpeak) within the esophageal ROI from pre-treatment to intra-treatment PET was compared between patients with grade 0-1 esophagitis and grade > 2 esophagitis using the Mann-Whitney test and binary logistic regression. Of 60 patients enrolled, 45 were evaluated. Reasons for exclusion included: did not complete both scans (n=8), re-irradiation within previous RT field (n=3), and feeding tube/stent prior to CRT (n=4). Forty-one patients were treated with definitive or neoadjuvant CRT and 4 palliative CRT. The median delivered RT dose was 46.8 Gy (range, 37.8-50.4 Gy). Grade 2 or greater esophagitis developed in 24 patients (53%) at a median of 28 days following CRT initiation. There was no significant difference in esophageal dosimetric parameters (max, mean, V35 Gy and V50 Gy) between patients with grade 0-1 and grade > 2 esophagitis. Among all patients the increase in esophageal SUVpeak (median) from pre-treatment to intra-treatment PET was 19% (interquartile range [IQR] -3.4-64%). The change in SUVpeak was significantly greater among patients with grade > 2 esophagitis compared to patients with grade 0-1 esophagitis, 40% (IQR 4.2-89%) vs -1.4% (IQR -8.7-45%), respectively (p=0.02). On univariate binary logistic regression analysis including clinical and dosimetric parameters, SUVpeak (HR 1.02, p=0.046) was the only significant variable. Esophageal SUVpeak increased on intra-treatment PET/CT performed during CRT for esophageal cancer and may predict for clinically significant RT-induced esophagitis.