Even Local Control of Metastatic Lung Tumors Is Worse Than That of Primary Lung Cancer in Patients Treated With Stereotactic Body Radiation Therapy

Abstract

The purpose of the present study was to determine the prognostic factors associated with local control (LC) and overall survival (OS) after Stereotactic Body Radiation Therapy (SBRT) for primary lung cancer and metastatic lung tumors. We retrospectively reviewed a total of 229 lung tumors in 201 patients (172 primary lung cancers in 164 patients and 57 metastatic lung tumors in 37 patients) who received SBRT between January 2001 and December 2011 in our institution. The median age of the patients was 76 years (range, 25-92 years). The median tumor diameter was 2.2 cm (range, 0.9-4.7 cm). SBRT of 45 Gy in 3 fractions, 48 Gy in 4 fractions, 60 Gy in 8 fractions or 60 Gy in 15 fractions was prescribed at the isocenter. SBRT was delivered with a linear accelerator using non-coplanar static 6 MV X-ray beams, typically using 4 non-coplanar and 3 coplanar static beams. Prognostic factors for LC and OS were analyzed using a Cox proportional hazards model. Statistical significance was defined as a value of p<0.05 in the present study. The present study was reviewed and approved by our Institutional Review Board. The median follow-up period was 41.9 months. The 3-year LC and OS rates were 72.5% (95% confidence interval[Cl]: 65.3-78.8) and 60.9% (95% Cl: 53.6-67.7), respectively, and the 5-year LC and OS rates were 67.8% (95% Cl: 59.6-75.1) and 38.1% (95% Cl: 30.3-46.5), respectively. Radiation pneumonitis of grades 2, 3 and 5 occurred in 22 patients, 6 patients and 1 patient, respectively. Multivariate analyses revealed that tumor origin (primary lung cancer vs metastatic lung tumor, HR = 0.30 [95% Cl: 0.15-0.62], p = 0.0013), tumor diameter (HR = 1.75 [95% Cl: 1.21-2.48], p = 0.0027), date of treatment (2001-2005 vs 2006-2011, HR = 2.00 [95% Cl: 1.07-3.81], p = 0.0275) and SBRT dose per fraction (HR = 0.51 [95% Cl:0.28-0.94], p = 0.0325) were significant independent predictors for LC and that gender (HR = 0.56 [95% Cl:0.34-0.88], p = 0.0125), tumor origin (HR = 0.45 [95% Cl: 0.28-0.73], p = 0.0018) and tumor diameter (HR = 1.70 [95% Cl: 1.30-2.21], p = 0.0001) were significant independent predictors for OS. SBRT resulted in good LC and tolerable treatment-related toxicities. Tumor origin and tumor diameter were independent predictors for LC and OS. The results suggest that dose escalation and/or additional therapy after SBRT when possible might improve both LC and OS for larger or metastatic lung tumors.