Safety and Efficacy of Stereotactic Body Radiotherapy in Ultracentral Lung Tumors Using a Risk-optimized Fractionation Scheme.

Background: Delivery of stereotactic body radiotherapy (SBRT) to ultracentral lung tumors remains a major challenge, with potentially excessive SBRT-related toxicity. This study investigates a risk-optimized approach to ultracentral SBRT in an elderly and comorbid patient cohort.
Patients and Methods: Analysis encompassed 129 patients (mean age: 70 ± 11 years, median Charlson comorbidity index: 4 [range, 3-5]) following risk-adapted SBRT to central or ultracentral primary and secondary lung tumors between 2012 and 2019 (78 central, 51 ultracentral). Ultracentral tumors were defined by planning target volume overlap with the proximal bronchial tree. Whereas ultracentral tumors were treated with a risk-optimized fractionation scheme of 50 Gy in 10 fractions, central tumors received higher-fractionated 60 Gy in 8 fractions. Outcome parameters and toxicity for ultracentral and central tumors were assessed using Kaplan-Meier and competing risk analyses.
Results: Local failure rate was not significantly increased in ultracentral tumors compared with central tumors (2-year local failure rate ultracentral, 26.9%; 95% confidence interval [CI], 12.2%-44.2%; central, 14.6%; 95% CI, 6.6%-25.5%; P = .17). Overall survival was similar in both groups (2-year overall survival central, 55.4%; 95% CI, 44.5%-68.9%; ultracentral, 54.9%; 95% CI, 40.8%-73.9%; P = .6). Toxicity was moderate, with toxicity ≥ grade 3 rates of 15.3% (95% CI, 5.9%-28.9%) for ultracentral and 7.3% (95% CI, 2.7%-15.0%) for central tumors after 2 years (P = .27). No grade 4 toxicity and only 1 potential grade 5 toxicity were observed in the ultracentral cohort.
Conclusion: Risk-optimized SBRT to ultracentral lung tumors is a reasonably effective and safe treatment alternative in frail patients.
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