Improvement of Internal Tumor Volumes of Non-Small Cell Lung Cancer Patients for Radiation Treatment Planning Using Interpolated Average CT in PET/CT

Respiratory motion causes uncertainties in tumor edges on either computed tomography (CT) or positron emission tomography (PET) images and causes misalignment when registering PET and CT images. This phenomenon may cause radiation oncologists to delineate tumor volume inaccurately in radiotherapy treatment planning. The purpose of this study was to analyze radiology applications using interpolated average CT (IACT) as attenuation correction (AC) to diminish the occurrence of this scenario. Thirteen non-small cell lung cancer patients were recruited for the present comparison study. Each patient had full-inspiration, full-expiration CT images and free breathing PET images by an integrated PET/CT scan. IACT for AC in PET IACT was used to reduce the PET/CT misalignment. The standardized uptake value (SUV) correction with a low radiation dose was applied, and its tumor volume delineation was compared to those from HCT/PET HCT . The misalignment between the PET IACT and IACT was reduced when compared to the difference between PET HCT and HCT. The range of tumor motion was from 4 to 17 mm in the patient cohort. For HCT and PET HCT , correction was from 72% to 91%, while for IACT and PET IACT , correction was from 73% to 93% (*p<0.0001). The maximum and minimum differences in SUV max were 0.18% and 27.27% for PET HCT and PETIACT, respectively. The largest percentage differences in the tumor volumes between HCT/PET and IACT/PET were observed in tumors located in the lowest lobe of the lung. Internal tumor volume defined by functional information using IACT/PET IACT fusion images for lung cancer would reduce the inaccuracy of tumor delineation in radiation therapy planning.