The north American experience with stereotactic body radiation therapy in non-small cell lung cancer

INTRODUCTION: In North America, the majority of prospective investigation using stereotactic body radiation therapy (SBRT) for thoracic targets has been carried out treating medically inoperable patients with non-small cell lung cancer. METHODS: Because SBRT involves constructing very compact high-dose volumes within the lung for targeting cancer deposits, tumor position must be accurately assessed throughout the respiratory cycle. Measures to account for this motion, either by tracking (chasing), gating, or inhibition (breath hold and abdominal compression) must be used to avoid large margins of error that would expose uninvolved normal tissues. Sophisticated image guidance and related treatment delivery technology have been used primarily for the purpose of targeting the tumor with as low a radiation dose to the surrounding normal tissue as possible. RESULTS: Phase I dose escalation trials have been carried out in North America to achieve potent tumorcidal dose levels capable of eradicating tumors with high likelihood. These studies indicate a clear dose-response relationship for tumor control with escalating dose of SBRT. While late toxicity requires further careful assessment, acute and subacute toxicity are generally acceptable. Radiographic and local tissue effects consistent with bronchial or vascular damage and downstream collapse with fibrosis are common. While such radiographic changes are most often asymptomatic, more frequent and sometimes debilitating toxicity has been observed for patients with tumors near the central airways. CONCLUSIONS: Prospective trials using SBRT in North America have been able to identify potent tolerant dose levels and confirm their efficacy in patients with medically inoperable disease. Although mechanisms of this injury remain elusive, ongoing prospective trials offer the hope of finding the ideal application for SBRT in treating pulmonary targets.