ESTRO 2020 Abstract Book

S154 ESTRO 2020

Purpose or Objective The value of FDG-PET/CT after induction treatment in esophageal cancer (EC) is not clear and, nowadays, international guidelines differ in their recommendations. The aim of this study was to assess the role of FDG-PET/CT in response evaluation to neoadjuvant radiochemotherapy (RCTX) and determine whether the changes in FDG-PET/CT uptake between pre/ and post-induction treatment could be related to the response and outcomes. Material and Methods Fifty-six patients with locally advanced EC were evaluated retrospectively. All patients had 2 FDG-PET/CT studies, one before RCTX with PET/CT1 as a baseline and the other after treatment (PET/CT2). A team of experienced nuclear medicine physicians and radiologists defined whether persistence or non-persistence of disease. The PET images were evaluated qualitatively (visual inspection) and semiquantitatively (SUVs). Patients were classified into 3 groups: persistence of disease (PET/CT2 shows loco/regional disease or progression), complete metabolic response (SUVmax on PET/CT2 ≤3) and unspecific FDG uptake. Percentages of change in SUV were calculated as (PET/CT1-SUV – PET/CT2-SUV)x 100 / PET/CT1-SUV, and patients were divided into two groups according to the percentage of change in the SUV (≥75% and <75%). Results A significant difference was found between the persistence group and the non-persistence group regarding the median percentage change in SUVtumor (72.95% vs 54.12%; p=0.04) and in SUVnode (89.91% vs 59.91% p=0.04). A significant difference was also found in patients treated with radiochemotherapy (RCTX) between the persistence group and the no persistence group regarding the percentage change in SUVtumor (58.02% vs 78.59%), although it is known that radiotherapy induces an inflammatory reaction with increased FDG uptake. The group of ≥75% of change SUVtumor showed a median survival of 37.32 months (IC: 95% = 49.93-24.70) and the group of <75% of change SUVtumor showed a median survival of 18.39 months (IC: 95% = 25.14-11.65) (p=0.04). Conclusion Our findings indicate that PET/CT imaging might be a standard component of the reevaluation of all locally advanced EC patients, especially to identify patients with or without persistence of tumor disease and predict better survival in patients with a higher percentage of tumor change. PD-0300 Assessment of global lung glycolysis using FDG PET/CT in radiotherapy for esophageal cancer C. Hsu 1,2 , K. Lin 1,2 , S. Wang 2,3 , C. Yu 1,2 , S. Yang 1,2 , H. Lin 1,2 , W. Tsai 2,4 , T. Wu* 2 , P. Shueng* 1,5 1 Far Eastern Memorial Hospital, Department of Radiation Oncology, New Taipei City, Taiwan ; 2 National Yang-Ming University, Department of Biomedical Imaging and Radiological Sciences, Taipei, Taiwan ; 3 Far Eastern Memorial Hospital, Department of Nuclear Medicine, New Taipei City, Taiwan ; 4 Dalin Tzu Chi Hospital, Department of Radiation Oncology, Chiayi, Taiwan ; 5 National Yang-Ming University, Department of Medicine- School of Medicine, Taipei, Taiwan Purpose or Objective Novel arc-based radiotherapy including volumetric modulated arc therapy (VMAT) and tomotherapy provides highly conformal dose distribution. However, it may contribute to extensive low-dose distribution in lungs and result in potential complications such as radiation

pneumonitis. FDG PET/CT scan serves as a useful tool not only for tumor detection, radiotherapy target volume delineation but also for assessment of the inflammatory changes in normal organs. In this study, we aim to assess lung inflammation using the global lung glycolysis of pre- and post-treatment FDG PET/CT in novel dynamic arc- based radiotherapy for esophageal cancer (EC). Material and Methods This study consisted of 17 EC patients who received FDG PET/CT scans before and after curative arc-based radiotherapy (VMAT, n=8; tomotherapy, n=9) at one medical center from January 2014 to May 2017. Pre- and post-treatment FDG PET/CT images were fused with simulation CT in the radiotherapy treatment planning system [Figure 1 below]. Irradiated lung volumes, non- irradiated lung volumes, the partial arc angles, predicted lung V5 and related lung doses were identified in the VMAT and tomotherapy plans. The SUVmean, SUVmax and global lung glycolysis (GLG) of tumors and lungs were calculated [Figure 2 below]. The partial arc angles, related restricted angles and dosimetric parameters were analyzed.

Results As compared the irradiated lungs and non-irradiated lungs in the post-treatment FDG PET/CT of 17 EC patients, the SUVmean (right lung: 0.70 vs 0.57, p=0.002; left lung: 0.71 vs 0.57, p=0.040), and ILG (right lung: 949.70 vs 220.80, p=0.005; left lung: 726.05 vs 139.26, p=0.001) significantly increased in the lungs involved by the ranges of arcs. In the non-irradiated lung regions, there were no significant differences in lung inflammation, SUVmean or NLG between pre- and post-treatment. The SUVmean of irradiated lungs and ILG were highly correlated with the ranges of arcs in the dynamic arc-based radiotherapy for EC. Conclusion SUVmean of irradiated lungs and ILG between pre- and post-treatment FDG PET/CT significantly increased in the lungs involved by arcs in the dynamic arc-based radiotherapy for EC.