Single-Fraction Lung SBRT Outcomes for Tumors ≥ 3cm

Abstract

Toxicity and local control at 1 year were the primary and secondary endpoints, respectively, of two randomized phase II lung SBRT trials having a single fraction (SF-SBRT) arm. Median tumor size in these trials was 2 cm. We surveyed our institutional database to analyze outcomes for tumors 3 cm or greater. A survey from 2003-2022 of 2481 patients (pts) in an IRB-approved prospective registry yielded 61 pts [2.5%] treated with SF-SBRT for tumors > 3cm. SF-SBRT dose was either 34 Gy or 30 Gy in one fraction. Outcomes of interest included rates of local control (LC) as well as treatment-related toxicity graded per CTCAE version 4.0. Gray's test and Log rank test were used to assess significance for disease recurrence and overall survival (OS), respectively. For the 61 pts, median follow up interval was 12.2 months (m). Pt characteristics included: female (57.4%); median age 76.8 years (range 56.5-94.3); median KPS 80 (range 50-100); active smokers 11.5%; median body mass-index 25.8 (range 16.4-48.8). Tumor characteristics included: median diameter 3.3 cm (range 3.0-6.6) with tumor size cohorts (% of total) being: 3-3.9 cm (73.8%); 4-4.9 cm (21.3%); 5-6.6 cm (4.9%); median PET SUVmax 9.1 (range 1.7-41.5); 6.6% were oligometastatic and 3.3% oligoprogressive; 93.4% were biopsy-proven with adenocarcinoma being 45.9%; 49.2% abutted the chest wall. SF-SBRT dose was 34 Gy in 80.3% cases and 30 Gy in 19.7%. At analysis, toxicity of any grade/type was seen in 27.5% pts, with no > grade 3 cases; 6.6% of pts had grade 2 chest wall toxicity. Rates (in %) of local, lobar, nodal and distant failure were 1.7, 1.7, 13.1 and 21.3, respectively. There was no significant difference in failure by size cohort. Median OS was 33 m, with 1-year OS at 75%. When analyzed by cohort, OS significantly declined with increasing size (p = 0.0421) CONCLUSION: Local control and toxicity with SF-SBRT for tumors > 3cm is comparable to that seen with smaller tumors treated on randomized trials.