MA02.02 Toxicity of Lung SABR in Patients with Coexisting Interstitial Lung Disease

Patients with lung tumors and coexisting interstitial lung disease (ILD) are at increased risk of toxicity following stereotactic ablative radiotherapy (SABR). We report on our institutional experience with SABR in such patients. Institutional patients undergoing lung SABR with coexisting ILD were identified. ILD subtypes were determined by a pulmonologist specializing in ILD. From late 2015, patients were routinely counseled about the increased treatment risks. Magnetic resonance (MR-)guided SABR was used to reduce target volumes from 2016. Overall and progression-free survival (OS, PFS) were estimated using the Kaplan-Meier method, and dosimetric predictors of radiation pneumonitis (RP) were analyzed based on total lung minus planning target volumes (PTV). Twenty-four SABR patients treated for lung cancer (n=22) or metastasis (n=2) between 2007-2018 were identified. Median patient age was 74 years, and the commonest ILD diagnosis was idiopathic pulmonary fibrosis. The commonest fractionation schemes were 60 Gy in 8 fractions (n=11), or 55 Gy in 5 fractions (n=6), and SABR was delivered on a Linac (n=17) to a motion-encompassing internal target volume, or with MR-guided SABR (n=7). At median follow-up of 36.9 months (95% CI, 15.8 to not reached), median OS and PFS were 16.6 and 13.3 months, respectively, and 12-month local control was 88.9%. Five patients (20.8%) developed grade ≥3 RP, of which 3 (12.5%) were fatal. Patients with grade ≥3 RP had a higher total lung V20Gy, and a higher ipsilateral and total mean lung dose (MLDEQD2; Fig. 1) than those without (p