Lung cancer is one of the leading causes of cancer-related death in Taiwan. Recently, there are more treatment methods available which result in increased patient survival. Although adenocarcinoma and squ/amous cell carcinoma were both categorized as non-small cell lung cancer (NSCLC), the recent advancement of target therapy implied that these two histologies behave differently (Shah NT, et al. 2005; Sandler A, et al. 2006). Radiation therapy is an important method for locally advanced non-resectable non-small cell lung cancer (NSCLC). Computed tomography (CT) is the mainstay for evaluating lung cancer. The advance of multi-row detector CT (MDCT) provides volumetric acquisition within a breath hold, and enables detailed evaluation of tissue and organ perfusion with excellent resolution. Using this new technique with image post processing, excellent spatial resolution and functional perfusion information can be obtained simultaneously. Therefore, the purpose of this study is to explore not only the longitudinal change of lung cancer eligible for radiation therapy but also comparison of adenocarcinoma and squamous cell lung cancers using perfusion MDCT. Total twenty patients with histopathologically proved adenocarcinoma or squamous cell carcinoma will be enrolled in this study and receive longitudinal study for perfusion MDCT evaluation before, during radiation therapy and in early and late phases after complete radiation therapy. Two-compartment Patlak plotting will be used for processing the image data, and tumor blood volume and permeability will be derived. From this study, we expect to understand the change of tumor vascularity after radiation therapy and characters of treatment response of adenocarcinoma and squamous cell carcinoma in addition to the change of tumor size.