Target Delineation for Radiosurgery (Including Postoperative Cavity Radiosurgery) in Brain Metastases

Studies support the use of focal irradiation in a variety of clinical scenarios for patients with brain metastases (BMs), including single, multiple, and postresection. As such, more practitioners are performing stereotactic radiosurgery (SRS) in lieu of whole-brain radiotherapy (WBRT). SRS is characterized by a highly conformal isodose distribution, and as a result, proper target delineation is paramount to avoid a geographical miss. Magnetic resonance imaging (MRI) has played an important role in SRS as it provides far superior soft-tissue contrast compared to computed tomography. Moreover, advanced MRI techniques and higher magnetic field scanners are becoming routinely available, and its use in SRS will continue to evolve. Therefore, practitioners of SRS must be aware of the limitations of MRI including spatial distortion and CT-MRI misregistration. In this chapter, we will review the practical aspects of SRS in both de novo and postoperative scenarios, with particular attention to delineation of the BM and critical organs-at-risk.