STEREOTACTIC BODY RADIATION THERAPY (SBRT) FOR CLINICALLY INOPERABLE EARLY STAGE NON SMALL CELL LUNG CANCER (NSCLC). RETROSPECTIVE ANALYSIS OF OUTCOMES AND RADIATION DOSE EFFETIVENESS

Purpose: SBRT has been considered as standard treatment for early stage clinically inoperable NSCLC. Some retrospective series showed better local control with Biologic Efective Dose (BED) ≥ 100 Gy10. This retrospective series aims to report the uni Institutional clinical results with SBRT using two fractionation schedules. Methods: Retrospective analysis of 76 patients with NSCLC stages IA – IIA (T1aN0M0 – T2bN0M0) – AJCC 2017. All patient were staged with PET/CT and considered clinically inoperable. The median age was 78 years old and median tumor size was 2.2cm (range: 0.70cm to 5.0cm). Histological type was adenocarcinoma in 50 patients (68.5%), squamous cell carcinoma in 23(31.5%) and 3(4%) had no biopsy. Forty nine(64.5%) patients were treated with 48 Gy in 4 fractions(BED=105.6Gy10) and 27(35.5%) with 40 Gy in 4 fractions (BED=80Gy10). Radiation fractions were delivere twice a week. The use of lower dose was a physician decision for some patients with central located tumor or lesions close to the thoracic wall. The SBRT technique was performed using Novalis Classic Linac model and IGRT ExacTrac® system. Tumor size, hystological type and radiation dose were factors analysed for outcomes.Overall Survival, Disease Free Survival and Local Control were calculated by Kaplan- Meier method. Chi-squared testing was used to verify the significance of the factors. Results: With a median follow up of 19 months, the 2-year local control, disease free survival and overall survival were 83.1%, 60.3%, and 68.8%, respectively. Patients treated with BED=80Gy10 had inferior 2-year local control (70.7% Vs 90.7%; p=0.047). Tumor size and histology were not significant factors for local control. Patients with adenocarcinoma had better 2-year disease free survival compared with those with squamous cell (60.3% Vs 38.3%; p=0.023). Grade 1 and 2 pneumonitis occurred in 20 (23.2%) and 4 (5.3%) patients, respectively. Tumor larger than 3 cm was the only factor related to the incidence of grades 1 and 2 pneumonitis (52.2% Vs 22.6%; p=0.036). One patient developed rib fracture. No other late toxicity was observed. Conclusions: This retrospective analysis confirms that SBRT with BED larger than 100Gy10 is more effective for local control than lower level for early stage NSCLC. Patients with squamous cell tumors had worse disease free survival compared with adenocarcinoma. Late toxicity was low and comparable with the literature. The dose of 48 Gy in 4 fractions was effective and safe.