Stereotactic ablative radiotherapy for stage I NSCLC: Recent advances and controversies.

Stereotactic ablative radiotherapy (SABR) is a technique that has rapidly entered routine care for early-stage peripheral non-small cell lung cancer in many countries in the last decade. The adoption of SABR was partly stimulated by advances in the so-called 'image guided' radiotherapy delivery. In the last 2 years, a growing body of publications has reported on clinical outcomes, acute and late radiological changes after SABR, and sub-acute and late toxicity. The local control rates in many publications have exceeded 90% when tumors of up to 5 cm have been treated, with corresponding regional nodal failure rates of approximately 10%. However, these results are not universal: lower control rates reported by some authors serve to emphasize the importance of quality assurance in all steps of SABR treatment planning and delivery. High-grade toxicity is uncommon when so-called 'risk-adapted' fractionation schemes are applied; an approach which involves the use of lower daily doses and more fractions when critical normal organs are in the proximity of the tumor volume. This review will address the new data available on a number of controversial topics such as the treatment of patients without a tissue diagnosis of malignancy, data on SABR outcomes in patients with severe chronic obstructive airways disease, use of a classification system for late radiological changes post-SABR, late treatment-related toxicity, and the evidence to support a need for expert multi-disciplinary teams in the follow-up of such patients.