Special issue on intraoperative radiotherapy—guest editor’s preface

The considerable technical advancements of irradiation techniques over the past decade lead to an increased use of high(er) single doses with less side effects. In some cancers, stereotactic radiosurgery (SRS) or stereotactic body radiotherapy (SBRT) with high single doses to one or more lesions have proved to be equally (or even more) effective as surgery. However, the delivery of ablative doses in a single fraction bears more advantages than instantaneous sterilization of the treated volume: a variety of effects on non-irradiated cells that are located adjacent (bystander effect and cohort effect) and distant (abscopal effects) to the initial tumor site have been observed (1-3). Corresponding to this, there is also increasing evidence for systemic effects after high-dose radiotherapy in metastasized malignancies (4,5), whereas this effect may be further augmented by checkpoint inhibitors such as ipilimumab (6,7).