Target delineation of gross tumor volume for radiation therapy planning using fusion images of ¹⁸F-fluorodeoxyglucose positron emission tomography and computed tomography.

Modern radiation therapy planning (RTP) has been performed using a larger number of images obtained with computed tomography (CT), named 3-dimensional RTP. Recently, F-18-flurodeoxyglucose position emission tomography (FDG-PET) has been used for RTP. FDG-PET can often distinguish between benign and malignant lesions when CT and magnetic resonance cannot. Although FDG-PET images lack anatomical precision (Fig. 1A), fusion images of FDG-PET and CT (PET/CT) have been extremely useful for determining the active sites of malignant disease. Particularly for patients with non-small cell lung carcinoma, both primary lesions and active lymph node matastases are well recognized (Fig. 1B). With PET/CT, which yields fewer false-negative results, smaller target volumes for radiation therapy can be delineated than with other imaging modalities (Fig. 2). The small radiation field (Fig. 3) leads to less toxicity in normal tissue, allows high radiation dose to be administered, and improves local control.