Review of thoracic reirradiation with stereotactic body radiation therapy: A focus on toxicity risks

Reirradiation of thoracic malignancies is clinically challenging in balancing the risks and efficacy. Stereotactic body radiation therapy (SBRT) can facilitate ablative dosing of discrete targets while minimizing normal tissue exposure; thus, SBRT is an attractive, minimally invasive option to consider for patients with recurrent or new malignancies within a previously irradiated field. Published data are summarized from 28 studies on the use of SBRT for thoracic reirradiation. We review clinical outcomes with a primary focus on toxicity risks, dosimetric correlates of normal tissue complication probability (NTCP), and other factors that correlate with NTCP. Meaningful compilation of published data on reirradiation with SBRT is limited because of the retrospective nature of published studies, which include mostly small numbers of patients, with various clinical scenarios and SBRT dosing and techniques. Nevertheless, these studies show that thoracic reirradiation with SBRT is feasible, with relatively favorable outcomes. Yet, severe to fatal toxicities do occur, and dosimetric measures to predict severe toxicity are poorly characterized, necessitating further study to better characterize predictive factors for NTCP.