Emerging role of stereotactic radiotherapy (SRT) in the treatment of early stage non-small cell lung cancer

Patients with early stage non small cell lung cancer (NSCLC) have historically been treated by resection alone, with results that have been superior to the results seen with radiation alone. This reflects the selection bias inherent to any comparison of operative and non-operative patients but surgery remains preferred treatment option. However, relapse rate after surgery is significant. In addition, a large proportion of these patients are not amenable to surgery due to medical co-morbidities and co-existing illnesses. These patients typically undergo a course of conventional radiotherapy, which provides poor outcomes both in terms of local control and survival. Attempts at dose escalation have met with some success, but local failures remain common and further dose escalation is limited by unacceptable toxicities. SRT allows for the delivery of a very high dose of radiation to a precise target. SRT presents the challenge of organ motion throughout the respiratory cycle. We review methods to mitigate this problem using both frame-based and frameless techniques, implanted fiducial markers, respiratory gating or deep inspiratory breath hold, and image guidance. Clinical experience with lung SRT continues to grow. Toxicities have been surprisingly mild. Based on available evidence, SRT appears to be effective, convenient and well tolerated.