3498 - Impact of Thoracic Duct Radiation Dose on Survival and Lymphocytes in Inoperable Non-Small Cell Lung Cancer Patients with Radiotherapy for Primary Tumors
Presenter(s)
C. Hu1, X. Zhang2, Q. Li3, Z. Ma4, W. Yang5, X. Chen6, H. Li7, Y. Hu3, S. Su8, W. Ouyang9, and B. Lu3; 1Guizhou Medical University, Guiyang, Guizhou, China, 2Guihang Guiyang Hospital, Guiyang, Guizhou, China, 3Department of Oncology, The Affiliated Hospital of Guizhou Medical University,and the Affiliated Cancer Hospital of Guizhou Medical University, Guiyang, Guizhou, China, 4Department of Oncology, Affiliated cancer Hospital of Guizhou Medical University, Guiyang, China, 5Department of Oncology, Affiliated Hospital of Guizhou Medical University, and Guizhou Cancer Hospital, Guiyang, China, 6Department of Oncology, Affiliated Hospital of Guizhou Medical University,and Affiliated cancer Hospital of Guizhou Medical University., Guiyang, China, 7Department of Thoracic Oncology, Affiliated Hospital of Guizhou Medical University, and Guizhou Cancer Hospital, Guiyang, PR China;Teaching and Research Section of Oncology, Guizhou Medical University, Guiyang, PR China, Guiyang, China, 8Guizhou Cancer Hospital, Guiyang, Guizhou, China, 9Department of Oncology, Affiliated Hospital of Guizhou Medical University,and Affiliated cancer Hospital of Guizhou Medical University., Guiyang, Guizhou, China
Purpose/Objective(s): Investigation of the Impact of Thoracic Duct Radiation Dose on Survival and Lymphocytes in Inoperable Non-Small Cell Lung Cancer Treated with Radiotherapy for Primary Tumors
Materials/Methods:
Clinical data were retrospectively collected from 91 patients across two hospitals between September 1, 2020, and September 30, 2024. The cohort included patients with stage III NSCLC who achieved an initial response to concurrent chemoradiotherapy and subsequently received maintenance therapy with PD-1 or PD-L1 inhibitors, as well as patients with stage IV driver gene-negative NSCLC who responded to first-line chemotherapy combined with PD-1 or PD-L1 inhibitors and subsequently receiving radiotherapy to the primary tumor. The thoracic duct was delineated as a new organ at risk (OAR) The mean dose (Dmean) and maximum dose (Dmax) to the thoracic duct during definitive radiotherapy for the primary NSCLC tumor were recorded. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the relationship between Dmean, Dmax, and the occurrence of severe lymphopenia post-radiotherapy. The optimal cut-off values were determined using the Youden index. Patients were stratified based on these cut-off values. Depending on the data type, comparisons between groups were made using the independent samples t-test, Mann-Whitney U test, or chi-square test, as appropriate. Survival rates were calculated using the Kaplan-Meier method, and multivariate analysis was conducted using the Cox proportional hazards regression model. The objective was to assess whether dosimetric parameters of the thoracic duct influence patient survival and lymphocyte counts.Results: ROC curve analysis revealed that the optimal cut-off value for the Dmean to the thoracic duct was 2049.10 cGy (AUC=0.686, P=0.001), whereas the cut-off value for the Dmax was 5370.30 cGy (AUC=0.502, P=0.975). Based on these findings, patients were stratified according to the thoracic duct Dmean using a threshold of 20 Gy for subsequent survival analysis.
Survival outcomes were assessed with follow-up through December 2025. In the <20 Gy group versus the =20 Gy group, the median PFS was 34 months vs. 16 months; the 1- and 2-year PFS rates were 63.5% vs. 50.3% and 51.2% vs. 29.6%, respectively (?²=4.712, P=0.030), indicating a statistically significant difference. The OS was not reached in either group; the 1- and 2-year OS rates were 87.1% vs. 69.0% and 62.5% vs. 52.6%, respectively (?²=1.832, P=0.176), with no significant difference observed. Lymphocyte analysis demonstrated no significant difference in pre-radiotherapy lymphocyte counts between the two groups (P=0.866). However, post-radiotherapy lymphocyte counts differed significantly (P=0.015).Conclusion: Dmean <20 Gy may mitigate radiotherapy-induced damage to lymphocytes in the immune system and prolong PFS. Delineating the thoracic duct as an OAR to facilitate target volume reduction may be beneficial for subsequent maintenance immunotherapy.