2069 - Safety and Efficacy of Lung SBRT Alone or in Combination with Concurrent Systemic Therapies

S. Karipineni¹, W. L. Ho², S. Cen³, X. Lei³, and J. C. Ye⁴; ¹University of Southern California Keck School of Medicine, Los Angeles, CA, ²USF Morsani School of Medicine, Tampa, FL, ³Department of Radiology, University of Southern California Keck School of Medicine, Los Angeles, CA, ⁴Department of Radiation Oncology, University of Southern California Keck School of Medicine, Los Angeles, CA

Purpose/Objective(s): Radiation treatment can be used in combination with chemotherapy, immunotherapy, or targeted therapies in metastatic lung and non-lung cancers. However, the exact patient population and timing of treatments still lacks consensus. This retrospective study aims to analyze the effectiveness and toxicity profiles of lung stereotactic body radiation therapy (SBRT) alone or in combination with concurrent systemic therapies (SBRT-S). Materials/

Methods: Patient and treatment characteristics were extracted from electronic medical records for 270 patients receiving 347 lung treatments of either hypofractionated radiation therapy (HFRT), 8-15 fractions, or SBRT at a single institution from 2014 to 2023. Lung tumors were categorized as ultra-central (UC) if they had a planning target volume (PTV) overlapping the trachea, proximal bronchial tree (PBT), heart, great vessels, or esophagus. Central tumors (C) were defined as having a PTV within 2 cm of the PBT, and the rest were categorized as peripheral (P). SBRT-S was defined as any systemic therapy administered within 30 days of radiation. Kaplan-Meier curve with log rank test was performed to assess local failure and Chi-squared test was used for assessing differences in toxicity rates.
Results: 250 treatments were SBRT alone and 97 treatments were SBRT-s, 43 with chemotherapy, 53 with targeted therapy, and 22 with immune checkpoint inhibitors, with 21 receiving multiple therapies. In the SBRT group there were 102 early-stage or locally advanced lesions (52.8%) compared to 19 (24.5%) in the SBRT-s group (p<.01). At the patient level, 156 had primary lung tumors and 114 had non-lung primaries with lung metastases. Median follow-up was 26.9 months. 1-year and 2-year local control estimates for SBRT alone were 96.9% and 91.4% respectively compared to SBRT-s at 95.1% and 91.7% with no statistically significant difference (p = 0.18). Additionally, there were no statistically significant differences in rates of pneumonitis at 37.2% overall (p = 0.33, n = 68 grade 1, 56 grade 2, and 5 grade 3) or in rates of any grade 3 or above toxicities at 8.9% overall (p = 0.98). There were five grade 4 adverse events including respiratory failure, cardiac tamponade, and myocardial infarction (2 in SBRT alone, 3 in SBRT-S). Out of the three grade 5 adverse events, two patients suffered respiratory failure from lung infections, and one patient had pneumonitis progressing to respiratory failure within weeks of radiation (all in SBRT alone).
Conclusion: There were no noticeable differences in radiation specific toxicity or local failure rates when comparing patients receiving SBRT alone and SBRT in combination with concurrent systemic therapies. Both local failure and overall toxicity rates are likely driven by other factors such as PTV, BED, and other patient-related characteristics. Further analysis of specific prognostic factors will need to be performed.