3214 - Online Adaptive Radiotherapy Based Integrated CT-Linac for Limited-Stage Small Cell Lung Cancer: A Prospective Phase II Trial
Presenter(s)
B. DONG1, S. H. Zheng2, K. Chen3, and M. Chen4; 1Sun Yat-sen University Cancer Center, Guangzhou, China, 2State Key Laboratory of Oncology in South China, Sun Yat-sen University Cancer Center, Guangzhou 510060, P. R. China., Guangzhou, China, 3Department of Population Health Sciences, Duke University School of Medicine, Durham, NC, 4Department of Radiation Oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Sun Yat-sen University, Guangzhou, Guangdong, China
Purpose/Objective(s): Anatomical changes and displacement of lung cancer during radiotherapy might introduce discrepancies between planned and delivered doses. In this phase II study, we evaluated the feasibility and safety of integrated CT-linac based online adaptive radiotherapy (oART) in limited-stage small cell lung cancer (LS-SCLC).
Materials/Methods: The target volume and organ at risks (OAR) of 25 patients with LS-SCLC during concurrent chemoradiotherapy were contoured by daily CT scans. If systematic changes exceed the criteria pre-defined, an oART will be performed, wherein the gross tumor volumes (GTVs), planning target volumes (PTVs), and OARs based intelligent auto-contouring were contoured on the online four-dimensional fan-beam CT (4D-FBCT) images via automated deformable registration. The dose-volume histograms were quantitatively compared between the initial plan performed on the online CT images and adaptive plan superimposed with initial plan. Clinical endpoints included dosimetric discrepancy, pattern of treatment failure, incidence and severity of adverse events. The progression-free survival (PFS), local recurrence-free survival (LRFS), and metastasis-free survival (MFS) were calculated using the Kaplan-Meier method.
Results: All patients completed oART successfully, taking an average of 28 minutes and 34 seconds from the start of online CT simulation to the completion of beam delivery. By adapting to tumor and anatomical changes, the mean target coverage of PTV improved from 96.05% to 96.95% (p-value=0.086). The dosimetric parameters including V20, and V30 of total lung, V40 of the esophagus decreased significantly. Distant metastasis was the most common mode of failure in this study, with 9 (36%) patients developed brain, liver, or non-regional lymph node metastases during a median follow-up of 13.7 months. Local recurrence occurred in 3 (12%) patients, all of which were in-field local failure (progression within replanning PTV) rather than marginal recurrence (recurrence in initial PTV, and excluded from the replanning PTV). The PFS, LRFS and MFS at 1 year were 49.8%, 81.9% and 71.1%, respectively. Eight (32%) and thirteen (52%) patients, respectively, developed grade =2 acute radiation pneumonia and esophagitis during follow-up period, no grade 4 or higher adverse events observed.
Conclusion: We demonstrated that the implementation of oART base on 4D-FBCT of integrated CT-linac for LS-SCLC is feasible, and could improve target coverage without increasing tumor margin recurrence.