451 © Springer Nature Switzerland AG 2020 A. Conti et al. (eds.), CyberKnife NeuroRadiosurgery, https://doi.org/10.1007/978-3-030-50668-1_39 Re-irradiation of Spinal Metastases Emma M. Dunne, Timothy K. Nguyen, Jay Detsky, Mitchell Liu, Simon S. Lo, and Arjun Sahgal 39.1 Introduction It is estimated that 40% of all patients with can- cer will develop metastatic disease to the spine [1]. Local control (LC) is important given the increased risk of debilitating complications asso- ciated with progression, including neurological compromise and spinal cord compression upon disease progression. Though conventional exter- nal beam radiation therapy (cEBRT) can effec- tively palliate painful bone metastases at doses of 8 Gy in a single fraction (SF) or 20–30 Gy in mul- tiple fractions (MF), controversy still reigns over the optimal dose fractionation to achieve durable pain control in this setting [2]. Randomised tri- als of dose fractionation schedules with cEBRT have reported rates of pain relief ranging between 50 and 85% and complete response rates to pain of up to 20%. Caution is warranted interpret- ing these results due to the different defnitions of pain relief and pain measurement scales used throughout the trials. Notably, reirradiation rates of up to 42% and 24% with SF and MF regi- mens respectively were reported due to persistent or recurrent pain [3, 4]. In an era where novel targeted therapies and improved systemic treat- ment have been shown to extend patient survival, the role of durable salvage reirradiation is gain- ing traction with a particular focus on determin- ing the optimal dose and radiotherapy delivery platform. 39.2 The Evidence for Reirradiation In 2014, the Symptom Control (SC) phase III ran- domised controlled non-inferiority trial led by the Canadian Clinical Trials Group (CCTG) sought to compare the effcacy of 8 Gy in a SF or 20 Gy in MF (1:1 randomisation) in a group of patients who previously received palliative cEBRT for painful bone metastases. Of the 850 patients ran- domly assigned, 28% had metastatic disease to the spine. Previous spine cEBRT doses included 6, 7, or 8 Gy in a SF or MF regimens includ- ing 4.5 Gy × 4 fractions and 5 Gy × 5 fractions E. M. Dunne (*) BC Cancer—Vancouver Centre, Vancouver, BC, Canada T. K. Nguyen · J. Detsky · A. Sahgal Department of Radiation Oncology, Sunnybrook Health Sciences Centre and University of Toronto, Toronto, ON, Canada e-mail: timothy.nguyen@lhsc.on.ca; jay.detsky@sunnybrook.ca; Arjun.Sahgal@sunnybrook.ca M. Liu Department of Radiation Oncology, BC Cancer— Vancouver Centre, Vancouver, BC, Canada e-mail: mliu@bccancer.bc.ca S. S. Lo Department of Radiation Oncology, University of Washington, Seattle, WA, USA e-mail: simonslo@uw.edu 39