Stereotactic body radiotherapy for moderately central and ultra-central oligometastatic disease: Initial outcomes

•SBRT can be safely delivered to central and ultra-central thoracic oligometastases.•Adhering to OAR dose constraints resulted in low acute and late toxicity rates.•PTV coverage compromise does not appear to significantly affect control or survival. Delivery of SBRT to central thoracic tumours within 2 cm of the proximal bronchial tree (PBT), and especially ultra-central tumours which directly abut the PBT, has been controversial due to concerns about high risk of toxicity and treatment-related death when delivering high doses close to critical mediastinal structures. We present dosimetric and clinical outcomes from a group of oligometastatic patients treated with a risk-adapted SBRT approach. Between September 2015 and October 2018, 27 patients with 28 central thoracic oligometastases (6 moderately central, 22 ultra-central) were treated with 60 Gy in 8 fractions under online CBCT guidance. PTV dose was compromised where necessary to meet mandatory OAR constraints. Patients were followed up for toxicity and disease status. Mandatory OAR constraints were met in all cases; this required PTV coverage compromise in 23 cases, with V100% reduced to