ESTRO 2024 - Abstract Book

S1620

Clinical - Lung

ESTRO 2024

consolidation [1,2]. We aimed to evaluate the efficacy and safety of T-SBRT in patients with LA-NSCLC treated according to PACIFIC regimen.

Material/Methods:

In this multicentric (n=2) monoinstitutional study, we retrospectively included all adult patients presenting LA-NSCLC treated by chemoradiotherapy followed by at least 1 cycle of durvalumab, between July 2017 and January 2023. T SBRT group included all patient who received highly hypofractionated (≤10 fractions of ≥5Gy) treatment on primary tumor, before or after normofractionated mediastinal irradiation (NFRT). Remaining patients were included in T NFRT group. Progression-free survival (PFS) and overall survival (OS) were evaluated using Kaplan-Meier method and compared using Cox proportional hazard model. Variables with p-value <0.15 were included in multivariate analyses. As sensitivity analysis, propensity score matching (PSM) within a specified caliper distance of 0.2 was performed using a 1:3 nearest neighbor matching algorithm without replacement, with distances determined by logistic regression. PSM was based on sex, age, performance status, tobacco use, and disease stage, and Cox model was used with robust variance estimator. Sixteen and 87 patients were included in T-SBRT and T-NFRT groups, respectively. Most of them were male (70.9%), with median age of 62 years old (range, 27-84), presented adenocarcinoma (57.3%) and received concurrent chemotherapy (89.3%). While T- SBRT group included 11/16 (68.8%) stage ≤IIIA, no stage IIIC patients, and 14/16 (87.5%) peripherally located tumors, T-NFRT group mostly included stage IIIB (n=46, 52.9%) patients (p=0.03). All patients were treated using IMRT technics. Median normofractionated dose was 66Gy (IQR 60-66) in both groups. In T-SBRT group, 11/16 patients were treated in 5 fractions of 8.5 to 10Gy, and 5 patients were treated with 3 fractions of 16 to 18Gy, prescribed on 80%-isodose line. T-SBRT was either performed after (n=6) or before (n=10) mediastinal NFRT. After a median follow-up of 36.8 months (IQR 23.4-52.7), the 3-year PFS of T-SBRT and T-NFRT groups was 75% (95%CI 53.7-100) and 39.9% (95%CI 29.3-54.4) (p=0.083; Figure 1), and 3-year OS was 81.8% (95%CI 61.9-100) and 59.8% (95%CI 49-73.1) (p=0.094; Figure 1). In multivariate analysis, T-SBRT tended to be associated with longer PFS (HR=0.43, p=0.11) and OS (HR=0.34, p=0.15) (Table 1). Nevertheless, after PSM these differences were not significant (PFS: HR=0.57, p=0.31; OS: HR=0.51, p=0.41; Figure 1). During RT, acute grade 3 were experienced by 8/87 (9.2%) and 1/16 (6.3%) patients in T-NFRT and T-SBRT groups, respectively, all consisting of esophagitis. During durvalumab maintenance, grade 3 toxicities occurred in 11 (12.6%) and 1 (6.3%) patients in T NFRT and T-SBRT groups, respectively, including 6 pneumonitis (n=5 and n=1, respectively). No grade >3 toxicity occurred. Results:

Table 1. Univariate and multivariate analyses of progression-free survival and overall survival.