International Journal of Hematology and Oncology 2021, Vol 31, Num 3 Page(s): 185-191
Pre-Radiotherapy 18F FDG PET/CT Predicts High-Risk Subvolumes for Residual Disease in Patients with Non-Small Cell Lung Cancer

Gulnihan EREN1, Osman KUPIK2

1Sıtkı Kocman University Hospital, Department of Radiation Oncology, Mugla, TURKEY
2Sıtkı Kocman University Hospital, Department of Nuclear Medicine, Mugla, TURKEY

Keywords: 18F FDG PET/CT, Lung cancer, Radiotherapy, Residual malignancy
The appearance of residual disease in 18F-FDG-PET/CT after radiotherapy (RT) in non-small cell lung cancer (NSCLC) is associated with worse survival. The aim of this study was to demonstrate the corresponding subvolume of tumours in pre-RT 18F-FDG-PET/CT (PET1) in patients in whom residual tumour was seen in post-RT 18F-FDG-PET/CT (PET2) after definitive RT/chemoradiotherapy (CRT). Patients with inoperable stage I-III NSCLC and who received chemoradiotherapy and/or radiotherapy alone and had residual tumour in PET2 were included. After matching the SUV threshold (70%, 80%, and 90%) delineated image seen in PET2 with PET1, we manually increased the tumour threshold of volume of interest (VOI) in PET1. We found which SUV threshold (70%, 80%, 90%) delineated OI in PET2 corresponded to which tumour subvolume in PET1. Thirty patients were included in the analysis. The median subvolume threshold corresponding to a SUV threshold of 70% VOI in PET2 was 50% (range, 40-65%). The mean SUV subvolume threshold in PET1 corresponding to an 80% SUV threshold VOI in PET2 was 56.3±7.5% (range, 40-70%). The mean SUV subvolume threshold in PET1 corresponding to a 90% threshold VOI in PET2 was 64.5 ± 7.5% (range, 50-80%). Pre-RT 18F-FDG-PET/CT can predict highrisk subvolumes for residual disease after radiotherapy. Threshold values of SUVmax 50%, 56.3%, and 64.5% corresponded to high risk areas for residual disease in pre-RT 18F FDG PET/CT.