2959 - Feasibility Analysis of Omitting the Clinical Target Volume in Thoracic Radiotherapy for Locally Advanced Esophagus Cancer: A Propensity Score-Matched Cohort Study

D. J. Chen¹, J. Liang², W. Jiang³, M. Zhao⁴, J. Lu⁴, K. Xu⁵, T. Y. Li⁵, and H. Sun⁶; ¹National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital,Chinese Academy of Medical Sciences and Peking Union Medical College,Shenzhen,518116,China, ShenZhen, China, ²National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital,Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, Shenzhen, China, ³Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China, ⁴National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital,Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, ShenZhen, China, ⁵Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China, Shenzhen, China, ⁶Cancer hospital, Chinese Academy of Medical Sciences, Shenzhen Center, Shenzhen, China

Purpose/Objective(s): Previous studies indicated that the omission of the clinical target volume (CTV) in thoracic radiotherapy (TRT) under modern radiotherapy techniques could deliver sufficient dose coverage to subclinical regions and spare organs at risk. This study aims to investigate the feasibility of CTV-omitted TRT in locally advanced esophagus cancer (LAEC). Materials/

Methods: A total of 145 patients with LAEC who received TRT from December 8, 2018, to February 9, 2023 were retrospectively analyzed. There were 86 patients who received TRT with CTV and 59 patients who received TRT without CTV. The possible prognostic factors including gender, age, location, pathology, staging, prescribed dose, neoadjuvant therapy, concurrent therapy, and consolidation therapy were balanced using propensity score matching (PSM). In the arm with CTV, CTV was defined as the primary tumor plus a 3cm expansion superiorly and inferiorly along the esophagus and cardia including the scope of elective nodal regions. Planning target volume (PTV) was genetated from an extension of gross target volume (GTV) of 5mm. In the arm without CTV, planning gross target volume (PGTV) was generated from an extension of 3cm of primary tumor superiorly and inferiorly along the esophagus and cardia and 5mm of primary tumor and metastatic lymph nodes. Kaplan-Meier analysis was used to evaluate the overall survival (OS), local-regional relapse free survival (LRFS). Adverse events (AEs) including hematologic toxicities, treatment-related pneumonitis, esophagits and other AEs were compared between the two arms.
Results: After PSM, 85 patients were enrolled in the arm with CTV, 42 patients were enrolled in the arm without CTV. The dose prescription was 95% PTV/PGTV 40-66Gy/20-33fractions/4-7weeks. The incidence of local-regional relapse was 35.7 % in the arm without CTV and 41.9% in the arm with CTV (P = 0.393). The most common site of metastasis was the regional lymph node which accounted for 80% of the arm without CTV and 60% of the arm with CTV(P=0.005). The median LRFS was 21 months versus 20 months(p=0.531) and the median OS was 28.0 months versus 39.38 months(p=0.062) in the arm without CTV and the arm with CTV, respectively. The incidence of grade 3 or higher esophagitis was 21.4% in the arm without CTV, significantly lower than the rate of 32.6 % in the arm with CTV (P = 0.046). The incidence of treatment-related pneumonitis in the arm without CTV group was significantly lower than that in the arm with CTV(7.2% vs 24.4%, p=0.019). No significant difference was observed in the grade 3 or higher hematologic toxicities between the arm without CTV and the arm with CTV(21.4% vs 18.6%,p=0.705).
Conclusion: It is feasible to omit CTV to reduce treatment-related toxicities without compromising the LRFS and OS for LAEC treated with TRT. However, It should be noted that CTV omission could deliver a higher rate of regional lymph node relapse. More prospective studies are needed to explore the feasibility of CTV omission.