Patterns of Locoregional Pancreatic Cancer Recurrence After Total Neoadjuvant Therapy and Implications on Optimal Neoadjuvant Radiation Treatment Volumes.

Purpose: To generate a map of local recurrences after neoadjuvant chemotherapy and radiation (total neoadjuvant therapy or TNT) followed by surgical resection for pancreatic ductal adenocarcinoma (PDAC). Such recurrence patterns will serve to inform radiation treatment planning volumes that should be given in the neoadjuvant setting.

Methods: Locoregional recurrences following TNT followed by surgery treated between 2009-2022 were radiologically identified. Recurrences were individually segmented using MIM software and complied in a single base scan. All contour compilations were used to create a threshold contour encompassing 80% of recurrences among all patients, head only, and body/tail only. The distance between organs at risk and the threshold contour were measured to design an optimal clinical target volume (CTV) contour for patients treated with TNT. Recurrence patterns were also compared to existing adjuvant guidelines to assess coverage.

Results: A database of 484 patients managed with TNT for PDAC was queried. While locoregional recurrences were rare in this cohort, we identified eighty patients with either isolated locoregional or simultaneous local and distant recurrences. Patients with diagnostic imaging at the time of recurrence were identified. The majority of recurrences were partially in the field of published contouring guidelines or volumetric expansions off of vessels, and volumetric coverage was low for all. Common areas of recurrence include the aortico-diaphragmatic junction, retro-pancreatic duodenal nodal basin, and the region to the right of the superior mesenteric artery. A novel set of proposed neoadjuvant contours was designed to cover the central-most 80% of recurrences.

Conclusions: This is the largest collection of local/regional PDAC recurrences from a cohort of patients treated exclusively with TNT. Patterns of local/regional recurrence using TNT in PDAC vary significantly from those patients with PDAC treated with a surgery-first approach. Novel contouring guidelines presented herein can help to ensure optimal coverage of high risk regions and avoid reliance on the current adjuvant guidelines to guide treatment planning.