A proton primer to stereotactic lung radiotherapy

Stereotactic body radiation therapy (SBRT) is regarded as a safe and effective treatment for early stage non-small cell lung cancer (NSCLC). However, the safety of SBRT has been questioned, specifically in the treatment of central tumors abutting critical organs at risk (OARs), when treating large or multiple tumors or when re-irradiating. Due to these concerns, radiation with stereotactic body proton therapy (SBPT) has emerged as a possible alternative due to its potential to decrease dose to OARs. The Particle Therapy Cooperative Group (PTCOG) recommends consideration of SBPT for large or multiple tumors, central tumors and those close to critical OARs. However, proton irradiation can be associated with significant uncertainty due to tumor motion, tissue heterogeneity, set up error, or changes in patient anatomy, as well as variations in distal range linear energy transfer values. In this review, we discuss clinical outcomes data from prospective and retrospective studies evaluating the benefits and risks of SBPT, methods to address uncertainties associated with PBT, and future directions for research.