The impact of 18F-FDG PET/CT imaging on radiation treatment planning for patients with non-small cell lung cancer

1686.5 Objectives: Non-contrast CT is the standard of care for radiotherapy (RT) planning. There is evidence that FDG PET overlay over CT impacts delineation of the gross target volume (GTV), decreases the interobserver variability between radiation oncologists, and changes the treatment from curative to palliative. Most studies in patients with non-small cell lung cancer (NSCLC) have been performed using FDG PET superimposed to CT using software packages. The purpose of this study was to compare the performance of integrated FDG PET/CT imaging and radiation therapy CT for patients with NSCLC. Methods: Fifteen patients with NSCLC underwent a radiation planning non-contrasted CT of the chest and whole body PET/CT imaging with an integrated PET/4-slice CT system using a standard FDG PET protocol and low-dose CT without contrast. The patients were positioned in the same immobilization devices for all imaging. DICOM PET/CT images were transferred to the radiation planning system (Eclipse 6.5, Varian Medical Systems). The non-contrasted CT images were contoured by consensus of a radiologist and radiation oncologist. On the fused PET/CT images, the anatomical limits of the FDG-avid lesions were contoured by consensus of a nuclear physician and radiation oncologist. The GTVs were measured and compared. The lymph node metastases were recorded as a tumor volume separate from the primary tumor volume. The difference in GTV was considered significant if greater than 25%. Treatment was considered changed from curative to palliative if distant metastases were detected. Results: When FDG PET/CT was used for contouring compared to radiation planning CT, the primary tumor GTV was decreased in 33% by differentiating atelectasis/post-obstructive pneumonia from tumor and increased in 20% of patients detecting additional tumor burden. An increased nodal disease burden was detected in 27% of patients. The use of PET/CT changed treatment from curative palliative by detecting distant metastases in 20% of patients. Conclusions: Integrated PET/CT imaging is a promising tool in RT planning. In this preliminary study on patients with NSCLC, contouring on PET/CT compared to CT alone changed the GTV in 53% of patients and treatment changed from curative to palliative in 20% due to detection of distant metastases.