2206 - The Effects of Irradiating the Triangle Volume for Locally Advanced and Borderline Resectable Pancreatic Adenocarcinoma in Patients with Poor Response to Chemotherapy
Presenter(s)
S. Sehgal1, S. Ke2, C. Hu3, C. Hill3, A. V. Reddy4, S. Mao5, T. A. Lin6, J. He7, J. J. Meyer3, and A. Narang8; 1Johns Hopkins Medical Institute, Department of Radiation Oncology, Baltimore, MD, 2Johns Hopkins School of Medicine, Division of Quantatative Sciences, Baltimore, MD, 3Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, 4Northside Radiation Oncology Consultants, Canton, GA, 5George Washington Medical Faculty Associates, Washington DC, DC, 6Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 7Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD, 8Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins Medicine, Baltimore, MD
Purpose/Objective(s): In patients with borderline resectable or locally advanced pancreatic cancer (BRPC/LAPC) who undergo resection following neoadjuvant chemotherapy, the role of pre-operative radiation remains controversial, as does optimal target volume design. Following patterns of failure analysis at our institution, we employed a systematic change in 2021 with respect to target volume design, transitioning from targeting only gross disease and involved vasculature to elective targeting of the “Triangle,” namely the space between celiac, superior mesenteric, and common hepatic arteries and portal/superior mesenteric veins. Herein, we explore locoregional control outcomes before and after this change as a descriptive, hypothesis-generating evaluation of locoregional control.
Materials/Methods: This was a single institution retrospective review of patients with BRPC/LAPC treated with neoadjuvant chemotherapy followed by stereotactic body radiation therapy (SBRT), with or without Triangle volume coverage, followed by resection. Patients treated between 2016 and 2022 were identified to allow adequate follow-up assessment. Primary endpoint was locoregional progression-free survival (LPFS), defined as end of SBRT to local recurrence or death. Factors associated with LPFS were identified in cohorts treated before and after institution of targeting the Triangle volume. Outcomes in high-risk subsets were further characterized.
Results: 203 patients met the inclusion criteria, out of which 48 received elective radiation to the triangle volume. Median age was 65.6 years (range, 39.5 – 83.9 years). Median duration of chemotherapy was 4 months (range, 1-18 months). Median SBRT dose was 33 Gy in 5 fractions (range, 30-40 Gy). In patients treated with SBRT to gross disease and involved vasculature only, univariate Cox regression showed that pathologic response to chemotherapy and nodal status were predictors of LPFS, (p=0.001, HR: 5.03, 1.87-13.57). In the Triangle cohort, corresponding associations were attenuated with wide uncertainty, consistent with possible effect modification, but hypothesis-generating given era-based confounding and limited sample size. In patients with moderate, poor, or no pathologic response and pathologic nodal positivity (n=81), those treated to only gross disease and involved vasculature (n=58) experienced 36-month LPFS and OS of 10.6% (CI 0.0497,0.2257) and 11.7% (CI 0.0557,0.2460), respectively, while those treated to the Triangle volume (n=23) experienced 36-month LPFS and OS of 17.4% (CI 0.0714, 0.4238) and 21.7% (CI 0.1001,0.4721), respectively.
Conclusion: In our
institutional cohort of BPRC/LAPC patients, elective targeting of the Triangle volume attenuated the adverse prognostic association of poor neoadjuvant systemic response with locoregional control, but findings are descriptive and hypothesis-generating. More prospective data is needed to define optimal patient selection for pre-operative therapy in this context.