Positron emission tomography (PET) is a 3-dimensional (3D) imaging technique that evaluates the level of physiologic and biochemical activity within tissue cells by measuring the distribution of an injected or inhaled radiotracer. Due to differences in metabolic rates, the concentration of radiotracers within cancerous cells differs from the concentration in surrounding normal tissue cells. PET has been proposed as a tool for monitoring the response of tumors to treatment and in estimating survival in patients with lung cancer.