Dose coverage impacts local control in ultra-central lung oligometastases treated with stereotactic radiotherapy

The use of Stereotactic Body Radiotherapy (SBRT) is controversial in Ultra-Central lung tumors, a subset of central lung tumors characterized by proximity to critical mediastinal structures. This is of interest in oligometastatic (≤3 metastases) patients, who can yield survival benefit from local treatments. The aim of our study is to assess the determinants of efficacy and toxicity in this setting. Clinical and dosimetric parameters were reviewed in a cohort of oligometastatic patients treated with SBRT for ultra-central tumors. Local control rate (LC) and toxicity were assessed. Statistical Analysis was carried out to assess the impact of those predictors on local recurrence and adverse events. One-hundred-nine consecutive patients were included. A median Biologic Effective Dose (BED) of 105 (75–132) Gy10 was prescribed. At a median follow-up of 17 (range 3–78) months, 2-year LC was 87%. Improved LC was correlated to Planning Treatment Volume (PTV) covered by 95% of the prescription dose (V95% PTV) > 85% (HR 0.15, 95%CI 0.05–0.49, p = 0.0017) and to Gross Tumor Volume (GTV) < 90 cm${}^3$ (HR 0.2, 95%CI 0.07–0.56, p = 0.0021). Overall and grade ≥ 3 toxicity incidence was 20% and 5%, respectively. Patients experiencing acute and late toxicities received significantly higher dose to 1 m${}^3$ (D1m${}^3$) of esophagus and lung volume receiving ≥5 Gy (V5Gy) (p = 0.016 and p = 0.013), and higher dose to 0.1 m${}^3$ (D0.1m${}^3$) of heart (p = 0.036), respectively. V95% PTV > 85% and GTV < 90 m${}^3$ are independent predictors of LC. Dose to esophagus, lung and heart should be carefully assessed to minimize treatment-related toxicities.