Respiratory gating and tumor tracking are two promising motion-adaptive lung cancer treatments, minimizing incidence and severity of normal tissues and precisely delivering radiation dose to the tumor. Accurate respiration measurement is important in respiratory-gated radiotherapy. Conventional gating techniques are either invasive to the body or bring insufficient accuracy and discomfort to the patients. In this paper, we present an accurate noncontact means of measuring respiration for the use in gated lung cancer radiotherapy. We also present an accurate tumor tracking technique for dynamical beam tracking radiotherapy. Two 2.4 GHz miniature radars were used to monitor the chest wall and abdominal movements simultaneously to get high resolution and enhanced parameter identification. Ray tracing technique was used to investigate the impact of antenna size in clinical practice. It is shown that our multiple radar system can reliably measure respiration signals for respiratory gating and accurate tumor tracking in motion-adaptive lung cancer radiotherapy.