2456 - Clinical Outcomes of Stereotactic Body Radiation Therapy (SBRT) for Centrally and Ultracentrally Located Early-Stage Lung Cancer

Purpose/Objective(s): Stereotactic body radiation therapy (SBRT) is a standard treatment for inoperable early-stage non-small cell lung cancer (NSCLC), offering excellent local tumor control (LC) while minimizing toxicity. However, treating centrally and ultracentrally located tumors remains challenging due to their proximity to critical structures such as major airways, the esophagus, and pulmonary vessels. The optimal radiation dose and fractionation schedule for these tumors remain uncertain, as higher doses may increase toxicity risks. This study evaluates clinical outcomes, including LC, overall survival (OS), and progression-free survival (PFS), in patients with centrally and ultracentrally located NSCLC and examines the impact of tumor size and radiation dose on survival.

Materials/Methods: We conducted a retrospective analysis of 103 patients (104 tumors) with early-stage NSCLC who received SBRT. The median age was 76 years (range: 49–90), with a high prevalence of smoking history (90.3%) and chronic obstructive pulmonary disease (78.7%). Tumors were evenly distributed between central (50.5%) and ultracentral (49.5%) locations. Patients were treated with either 50 Gy in 5 fractions (36.9%) or 60 Gy in 8 fractions (63.1%). Kaplan-Meier survival analysis and competing risk models were used to assess the impact of tumor location, size, and radiation dose on outcomes.

Results: At a median follow-up of 3.6 years, the 1-, 3-, and 5-year OS rates were 90.1%, 55.6%, and 31.4%, respectively. LC remained high, with 1-, 3-, and 5-year rates of 96.7%, 84.6%, and 77.8%. PFS rates at 1, 3, and 5 years were 86.9%, 60.5%, and 54.1%, respectively. No statistically significant differences in LC (p = 0.69), OS (p = 0.46), or PFS (p = 0.43) were observed between central and ultracentral tumors, though ultracentral tumors exhibited a numerical trend toward worse OS and PFS. Neither radiation dose (p = 0.87) nor tumor size (p = 0.66) significantly impacted outcomes. The primary pattern of failure was distant metastasis, while local and regional recurrences were uncommon, reinforcing SBRT’s efficacy in achieving durable LC.

Conclusion: SBRT provides durable LC and favorable survival outcomes for centrally and ultracentrally located early-stage NSCLC. While ultracentral tumors showed a trend toward worse OS and PFS, this did not reach statistical significance. The lack of a clear relationship between outcomes and radiation dose or tumor size suggests that other factors, such as tumor biology or comorbidities, may influence prognosis. Future research should focus on optimizing treatment strategies, balancing tumor control with toxicity risks, and exploring the role of systemic therapy to improve long-term outcomes in this high-risk population.