Abstract 864: Increased rates of radiation pneumonitis in patients receiving stereotactic ablative radiotherapy for central versus peripheral lung tumors

Abstract

Abstract Purpose: Treatment of central lung tumors with stereotactic ablative radiotherapy (SABR) has been associated with higher rates of toxicities than patients with peripheral tumors. Here we report our institution's experience in treating central lung tumor patients with SABR, compared to patients treated for peripheral lung tumors. Methods: We retrospectively reviewed outcomes in 82 patients with a total of 96 primary or metastatic lung tumors treated by SABR. The cohort included 47 central and 49 peripheral tumors and all were treated with 50 Gy in 4-5 fractions. Outcomes and radiation-associated toxicities were compared between the two groups, not including patients in whom central and peripheral tumors were concurrently treated (8 such patients). Dosimetric analysis was performed on patients with central tumors to determine max point dose (MPD) and volumetric max dose (Vmax) to central structures. Results: Median follow-up time was 15 months (range 1 to 59 months). Median overall survival was 34 and 40 months (p=0.75) for patients with central and peripheral tumors, respectively. We observed no hemoptysis and no grade 5 toxicities. Rates of symptomatic toxicity were higher in patients with central tumors (grade 2+, 38% vs. 11%, p=0.0056) but were equivalent for severe toxicity (grade 3+, 5.4% vs. 5.4%, p=0.93). The vast majority of toxicities were due to radiation pneumonitis, incidence of which was significantly greater in patients with central tumors (grade 2+, 30% vs. 2.7%, p=0.0021; grade 3+, 5.4% vs. 0%, p=0.15). Dosimetric analysis of 36 central tumor treatment plans revealed that 23 (64%) exceeded at least one of the dose constraints used in RTOG 0813, most commonly for central airway. Rates of grade 2+ pneumonitis were not significantly different between patients exceeding RTOG 0813 central airway dosing constraints vs. those meeting them (24% vs. 20%, p=0.69), but trended towards significance for grade 3+ radiation pneumonitis, with patients exceeding RTOG 0813 central airway dosing constraints experiencing higher rates (0% vs. 13%, p=0.095). Conclusions: Central lung tumor patients treated with SABR appear to have greater risk for symptomatic radiation pneumonitis than patients with peripheral tumors. Exceeding RTOG 0813 dosimetric constraints for central airway may predispose to higher risk for severe radiation pneumonitis. Citation Format: Aadel A. Chaudhuri, Chad Tang, Nicholas Trakul, Jacob Wynne, Billy Loo, Maximilian Diehn. Increased rates of radiation pneumonitis in patients receiving stereotactic ablative radiotherapy for central versus peripheral lung tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 864. doi:10.1158/1538-7445.AM2014-864