Dosimetric and Clinical Factors Associated with Local Control in Stereotactic Body Radiotherapy-Treated Early-Stage Non-Small Cell Lung Cancer: A Single Institution Analysis

Summary: Stereotactic body radiotherapy (SBRT) has become more widely accepted as a standard of care for early-stage, non-small cell lung cancer (NSCLC) given its acceptable local control (LC) rates and minimal toxicity. However, there remains a need for more clinically informed treatment delivery guidelines as well as more comprehensive risk stratification criteria. In this abstract, we demonstrate the impact of several dosimetric parameters and tumor characteristics, most of which are seldom described in the literature, on LC and overall disease control in SBRT-treated, early-stage NSCLC. We retrospectively reviewed patients with early-stage (T1-T3N0) NSCLC who received lung SBRT in 1-5 fractions within one academic healthcare system from 1/1/2015-12/31/2021. Kaplan-Meier method and cumulative incidence models were used to estimate outcomes. 195 lesions from 185 patients were included. Treated lesions were 73.3% peripheral, 23.6% central, and 3% ultracentral with median maximum dimension of 1.6cm [IQR 1.2-2.2]. Median dose was 50Gy [IQR 48-50] with a median BED of 105.6 [IQR 100-105.6]. Median follow-up time of 32 months [IQR 17-45]. LC rates at 12- and 24-months posttreatment were 98.5% and 95.4%, respectively. Regional control (RC) and distant control (DC) rates at 2-years were 88.8% and 91.3%, respectively. Smaller internal gross tumor volume (iGTV), smaller planning target volume (PTV), absence of a previous lung cancer diagnosis, presence of synchronous primary lung tumors, receipt of greater than 110% and 120% of the prescribed dose, and higher minimum dose covering 99% of the iGTV volume (D99%) were each associated with improved LC (p 30 ccs at 52.9% and 63.8%, respectively. Tumor location, PET/CT standardized uptake value (SUV), and daily versus every other day fractionation did not affect local or regional control. Grade 3, 2, and 1 toxicity rates were 0%, 6%, 21%, respectively and were mostly limited to fatigue and dyspnea. When treating early-stage NSCLC with SBRT, attention to radiotherapy plan design, including minimum iGTV coverage and higher maximum dose may lead to higher rates of control. Careful considerations should be made for both large and smaller than average PTVs as standard guidelines may compromise control.