Ten Fraction Ultra-Central Thoracic Hypofractionated Stereotactic Body Radiotherapy (hfSBRT): An Analysis of Outcomes, Dosimetry, and Toxicity.

Purpose/Objective(s) Treatment of ultra-central thoracic tumors, defined as tumors in which direct tumor abutment or planning target volume (PTV) overlap with the primary bronchial tree, great vessels or esophagus exists, remains challenging due to concern for treatment related toxicity and relative lack of dosimetric data to organs at risk (OARs). We report clinical outcomes, toxicity and dosimetric data for ultra-centrally located tumors. Materials/Methods Sixty-one ultra-centrally located lung tumors treated at a single institution between November 2009 and March 2017 were retrospectively reviewed. Overall survival (OS), progression free survival (PFS), and local control (LC) were calculated. Incidence and grade of treatment related toxicity were evaluated. Treatment dosimetry was analyzed. Results Median age at time of treatment was 70 years (38 to 96 years). Median follow up time was 14 months (1 to 102 months). Individuals underwent hfSBRT for primary (n = 21, 34%), limited metastatic (n = 17, 28%), or recurrent (n = 23, 38%) disease. Median treatment dose was 65 Gy (40 to 70 Gy), corresponding to a biologically effective dose (BED) of 107.25 Gy (56 to 119 Gy). Median PTV was 66cc (4 to 592cc). One- and three-year OS, PFS, and LC were 60%/24%, 37%/19%, and 84%/62% respectively. On univariate analysis, only treatment of locally recurrent disease was negatively correlated with LC (P = 0.026). This did not translate to inferior PFS or OS (P = 0.34 and 0.49 respectively). Median esophageal, maximum dose (Dmax) was 35 Gy, with a median V40 of 0cc. Median primary bronchial tree Dmax was 60 Gy, with a median V52 of 1.05cc. Median great vessel Dmax was 71 Gy, with a median V55.7 of 0.42cc. Grade 2 or higher pneumonitis was reported in 12 individuals (20%). This corresponded to 13% of individuals undergoing initial hfSBRT, and 30% of individuals undergoing re-irradiation (P = 0.09). Grade 3 or higher toxicity was reported in seven individuals (11%). This correlated to two grade 3 incidences of pneumonitis (one re-irradiation, one initial hfSBRT), one grade 3 esophagitis during re-irradiation (Dmax of 57.8 and V40 of 6.3cc), one grade 3 bronchial/tracheal fistula during initial hfSBRT (Dmax of 79.1 and V52 of 3.68cc), and three grade 5 hemoptysis events (all during re-irradiation). One hemoptysis event was categorized as “possibly” related to treatment, while the remaining two events were categorized as “unlikely” related to treatment with clear bronchoscopic or radiographic evidence of disease progression identified. Conclusion Our results demonstrate that 10-fraction ultra-central thoracic SBRT can be effectively administered with high rates of LC, favorable dosimetry, and acceptable rates of toxicity. Caution with re-treatment of ultracentral disease must be taken as this may be associated with increased toxicity, and inferior tumor control.