Distinguishing Radiation Pneumonitis from Local Tumour Recurrence Following SBRT for Lung Cancer

: Radiation pneumonitis is one of the most common toxicities following SBRT for lung cancer. Although local control rates are good, a recurrent tumour is dif fi cult to distinguish from radiation pneumonitis due to similar size and morphology. Therefore, early detection of a recurrent tumour is challenging, and moreover, it is crucial for affected patients, as early detection enables curative salvage therapy. Promising data exists to solve these challenges for late recurrences, for example, the analysis of high-risk CT features allows prediction of recurrence after 12 months. But particularly in cases of early recurrences and radiation pneumonitis, comprehensive data are lacking. Therefore, the aim of this study was to review the existing literature with special regard to radiological response assessment after stereotactic body radiotherapy and risk factors for predicting radiation pneumonitis or local recurrence. (PET) is encouraging. Huang et al developed a follow-up algorithm for response-assessment after SBRT, in which a PET is recommended in some cases, and Dong et al demonstrated that patients with high metabolic activity (described as SUVmax) before treatment had a worse overall survival. Nevertheless, the interpretation of a PET-scan should be done carefully as there is no optimal SUVmax threshold for predicting local recurrence or radiation pneumonitis. Another approach is to analyse of dosimetric parameters before performing SBRT, and indeed, some parameters seem to be associated with radiation pneumonitis, but again no speci fi c dose constraints are found yet. We found promising data in the literature, but the results are controversial, and a conclusion could not be drawn.