Biologically Effective Dose as a Predictor of Radiosurgery Treatment Outcomes for Pulmonary Metastases

Abstract

<h3>Purpose/Objective(s)</h3> As targeted therapy for oligometastatic disease becomes more widely accepted, continued investigation is needed to characterize predictors of treatment outcomes and better inform clinical management. In this abstract we describe how biologically effective dose (BED) impacts local control (LC), regional control (RC) distant control (DC), and overall survival (OS) in a cohort of patients receiving stereotactic body radiotherapy (SBRT) for metastatic and recurrent pulmonary lesions. <h3>Materials/Methods</h3> The study was undertaken via retrospective review at a single institution. Lung lesions in patients who underwent SBRT to pulmonary metastases from distant primaries or recurrent tumors from previously treated lung cancer were included. Only patients who were treated between 2016 and 2019 were included. Patients with newly diagnosed primary lung cancer manifesting as single pulmonary lesions were excluded. A two-proportion z-test was employed for statistical analysis. <h3>Results</h3> From a single institution, 246 treated metastatic lesions from 75 patients were included. A subset of 114 treated metastatic lesions from 41 patients received a BED < 80 Gy. A subset of 132 treated metastatic lesions from 66 patients received a BED of ≥ 80 Gy. SBRT was performed at a median BED of 57.6Gy (interquartile range [IQR], (38.4,60)]) for lesions receiving BED < 80Gy and at a median BED of 100Gy (IQR, 80-112.5) for lesions receiving BED ≥ 80Gy. Two-year LC was 82.5% (94/114) for lesions with BED <80Gy and 90.9% (120/132) for lesions with BED ≥ 80Gy (p=0.048). Two-year RC was 51.8% (59/114) for lesions with BED <80Gy and 56.8% (75/132) for lesions with BED ≥ 80Gy (p=0.424). Two-year DC was 48.2% (55/114) for lesions with BED <80Gy and 59.1% (78/132) for lesions with BED ≥ 80Gy (p=0.089). Two-year OS was 33.3% (38/114) for lesions with BED <80Gy and 60.6% (80/132) for lesions with BED ≥ 80Gy (p<0.0001). <h3>Conclusion</h3> When treating oligometastatic pulmonary lesions with SBRT, a BED of greater than or equal to 80Gy is associated with improved two-year LC and two-year OS to a statistically significant degree. However, no significant difference in two-year RC and DC is noted when using a BED greater than or equal to 80Gy. These results suggest that higher radiation doses are more effective when using SBRT to treat oligometastatic pulmonary lesions, and that a goal BED of 80 Gy or more should be pursued.