Flattening filter free stereotactic body radiation therapy for lung tumors: outcomes and predictive factors

Background: Stereotactic body radiation therapy (SBRT) using flattening filter free (FFF) has been commonly used, however, its outcomes and predictive factors in lung tumors are limiting. Thus, we aim to assess the clinical outcomes of this approach and identify factors associated with outcomes in patients with early stage non-small cell lung cancer (NSCLC) and oligometastatic/oligoprogressive lung tumor (OLT).

Methods: Patients who underwent lung SBRT with FFF were retrospectively reviewed. All patients were delivered using volumetric modulated arc therapy (VMAT) technique. The primary outcome was local control (LC). The secondary outcomes were overall survival (OS) and toxicities. We assessed the association between LC and various factors in OLT.

Results: From February 2014 to July 2019, ninety-four patients and 129 lesions with median follow-up time of 30 months were included in the analysis. Twenty-six patients with 26 lesions were early NSCLC, while 68 patients with 103 lesions were OLT, 41.7% of which were from colorectal cancers (CRC) and 18.5% were from primary lung cancers. Two-year LC was 88.9% and 85.7% for early NSCLC and OLT, respectively. Two-year OS was significantly higher for early NSCLC than OLT (83.3% vs. 68.7%, P=0.035). In the multivariate analysis for OLT, CRC origin (hazard ratio, HR 10.59, 95% CI: 2.29-48.95, P=0.003) and gross tumor volume (GTV) mean BED₁₀ ≤147 Gy (HR 5.16, 95% CI: 1.13-23.59, P=0.034) were significantly associated with higher local failure (LF). Most of the acute grade 1-2 toxicities were radiation pneumonitis (26.5%). No grade 3-5 event was observed.

Conclusions: This study confirmed the clinical efficacy and safety of lung SBRT using FFF-technique. Our findings support the role of using a high BED₁₀ regimen to achieve good LC for OLT and the potential role for dose escalation for primary CRC.