The RTOG opened in May 2004 a phase II trial of SBRT in the treatment of medically inoperable patients with stage I/II non-small cell lung cancer in an effort to determine if SBRT could achieve acceptable local control as seen in retrospective series.24, 26, 32-38 A secondary objective is to determine if this technique achieves acceptable treatment-related toxicity. In this trial, patients with T1, T2 (≤ 5 cm), or T3 (≤ 5 cm), N0, M0 medically inoperable non-small cell lung cancer are treated with SBRT to a total of 60 Gy in 3 fractions of 20 Gy each over 1.5 to 2 weeks. This protocol excludes patients with T3 tumors involving the central chest and structures of the mediastinum as well as patients with any T-stage tumor within or touching the zone of the proximal bronchial tree. This region is defined as a volume 2 cm in all directions around the proximal bronchial tree (carina, right and left main bronchi, right and left upper lobe bronchi, intermedius bronchus, right middle lobe bronchus, lingular bronchus, and right and left lower lobe bronchi).