2016 - Outcomes and Toxicity in Patients Treated with Stereotactic Body Radiation Therapy for Ultracentral Lung Tumors at a Single Institution

D. S. Buchberger¹, C. Busch², P. Xia¹, C. A. Reddy¹, K. L. Stephans³, and G. M. Videtic^2,3; ¹Department of Radiation Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH, ²Cleveland Clinic, Cleveland, OH, ³Department of Radiation Oncology, Cleveland Clinic, Cleveland, OH

Purpose/Objective(s): Stereotactic body radiation therapy (SBRT) for lung tumors is effective in treating definitive and oligo-progressive/oligometastatic lesions. Increased toxicity has been reported in treating ultracentral tumors and is an area of ongoing study. We report on outcomes and toxicity for ultracentral lung tumors treated at our institution. Materials/

Methods: For the interval 2014-2023, we surveyed our IRB-approved prospective registry for ultracentral tumors with a minimum of 6-months follow-up. This included tumors within 1 cm of the main bronchus, trachea, or lobar airways (ultracentral-airway; UC-A), or tumors with PTV overlap with esophagus, heart, and/or great vessels (ultracentral-non-airway; UC-NA). Statistical analysis was performed for outcomes including disease failure, survival, and toxicity.
Results: For the 9-year interval, 259 patients were identified: 113 (43.6%) patients as ultracentral-airway; 146 (56.3%) patients as ultracentral-non-airway. Median follow-up was 26.8 months. Median age was 72 years. 50.2% was female. 73.4% was treated definitively, 13.5% for oligometastatic disease, 6.6% for oligo-progressive disease, and 6.2% for salvage after surgery. Median tumor size and PET SUV max were 2.5 cm and 10.2, respectively. SBRT schedules were 50 Gy in 5 fractions (76.4%), 60 Gy in 8 fractions (5.4%), 60 Gy in 5 fractions (5.4%), and 34 Gy in 1 fraction (5.0%). Crude rates of local failure were 14.2% for UC-A tumors and 3.4% for UC-NA tumors. For all patients, 29.3% experienced any grade toxicity – 38.9% in the UC-A group, and 21.9% in the UC-NA group. There were 12 grade 3 toxicities (4.6%), 7 grade 4 toxicities (2.7%), and 2 grade 5 toxicities (0.77%; esophageal bleed, effusion/collapse) with both being UC-A patients. On multivariable analysis, only tumor size was significantly associated with toxicity (OR 1.40, 95% CI 1.61-1.69). On cumulative incidence analysis the median time to failure for all patients was 48.2 months, 41.4 months for the UC-A group, and was not reached in the UC-NA group. 54.0% of UC-A patients experienced disease failure compared to 44.5% of UC-NA patients. Median overall survival was 38.2 months for the entire cohort, 30.1 months for the ultracentral-airway group, and 48 months for the ultracentral-non-airway group. On Cox proportional hazards regression for overall survival, on multivariable analysis ultracentral subtype UC-A (HR 1.62, 95% CI 1.91-2.21) and KPS (HR 0.98, 95% CI 0.97-0.99) were significantly associated with survival.
Conclusion: Ultracentral tumors with proximity to airway have higher rates of disease failure and the potential for more severe toxicity compared to tumors with PTV overlap of the esophagus, heart, and great vessels without airway involvement. However, toxicity rates are low independent of location.