3487 - Initial Clinical Results of Four-Dimensional CT-Guided Online Adaptive Radiotherapy for Advanced Gastric Cancer
Presenter(s)
A. Huang1, H. Ma1, J. Gao1, D. Gao2, B. Hu1, and J. Han3; 1Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China, Wuhan, China, 2Shanghai United Imaging Healthcare Co., Ltd. Shanghai, 201807, China, Shanghai, China, 3Institute of Radiation Oncology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
Purpose/Objective(s): Due to gastric fullness status and respiratory motion, target deviation is a major factor affecting the efficacy of radiotherapy for gastric cancer. Therefore, Radiotherapy for the primary gastric lesion during the treatment of advanced gastric cancer is highly controversial. Four-dimensional (4D) CT-guided online adaptive radiotherapy (ART) shows potential to assess respiratory motion on target of gastric cancer and enable timely target adjustments, thus improving the precision of radiotherapy. The aim of our study is to evaluate the effectiveness, safety and prognosis factors of 4DCT-guided online ART for advanced refractory gastric cancer
Materials/Methods: This is a prospective observational study enrolling patients with advanced gastric cancer who have progressed after standard treatments, including oxaliplatin- and taxane-based chemotherapy with or without immunotherapy. The progression should include gastric lesions and the presence of evaluable extra-gastric lesions. Treatment involves physician-selected subsequent-line systemic therapy combined with radiotherapy (40-45 Gy/25 fractions) for the gastric lesions and high-risk perigastric lymph node regions treated. During radiotherapy, 4DCT-guided online ART based on the uRT-linac 506c was necessary and applied according to the target deviation. The primary endpoint was progression-free survival (PFS), while secondary endpoints included overall survival (OS), in-field response rate, out-of-field response rate, and meanwhile exploratory analysis of clinical and immunological characteristics as well as safety assessment were performed.
Results: 20 patients were enrolled from July 2023 to February 2025. 16 patients completed ART and received the first time evaluation. Although, 5 patients(31.3%) progressed after second-line therapy, and 11 patients(68.7% )recieved PD1 inhibitor before. the in-field response evaluation showed a partial response (PR) rate of 56.2 %, while the out-of-field disease control rate (DCR) reached 62.5% . Six patients experienced out-of-field progressive disease (PD). Median PFS was 9.5 months (95% CI 7.4-11.5). Further analysis revealed minimal changes in hemoglobin levels or tumor markers (CEA and CA199) before and after radiotherapy. Howerve, CD4 cells showed a mild decrease after radiotherapy, while CD8 cells exhibited a significant increase two months after radiotherapy (38.6 VS. 26.7,P<0.001). The inflammatory cytokine IL-10 decreased significantly after radiotherapy (3.9 VS. 5.9, P=0.04). Treatment-related adverse events were grade 1-2 gastrointestinal reactions, and one patient showed grade 3 thrombocytopenia.
Conclusion: For advanced gastric cancer patients progressed after standard treatments, the combination of ART and systemic therapy demonstrated benefits in efficacy and survival with manageable toxicity. Additionally, online ART could modify tumor immune microenvironment, and further research to confirm our findings