Location, Location, Location: What Should be Targeted Beyond Gross Disease for Localized Pancreatic Ductal Adenocarcinoma? Proposal of a Standardized Clinical Tumor Volume for Pancreatic Ductal Adenocarcinoma of the Head: The “Triangle Volume”

Abstract

Purpose/Objective(s)

In patients with borderline resectable or locally advanced pancreatic adenocarcinoma (BRPC/LAPC), local failure rates after resection remain significant, even in the setting of neoadjuvant chemotherapy and radiation. Sub-optimal local control may relate to variable radiation target delineation, as no consensus exists around clinical tumor volume (CTV) design in this context. In the surgical literature, recent attention has been given to the "Triangle" volume (TV) as a source of subclinical, residual disease. In order to understand whether the TV can inform optimal CTV design, we mapped locoregional failures after resection in a large cohort of BRPC/LAPC patients and compared locations of failure to the TV.

Materials/Methods

Patients with BRPC/LAPC of the head/neck diagnosed between 2016-2019 who developed locoregional failure after surgery following neoadjuvant chemotherapy and radiation were identified. Descriptive statistics were generated to report the frequency of locoregional failures located within the TV and the frequency of new vascular involvement at time of failure, as compared to vascular involvement at diagnosis. Additionally, dosimetric coverage of the TV with the pre-operative radiation plan that had been utilized was assessed.

Results

In 31 patients who experienced locoregional failure, the centroid of failure was located within the TV in 28 cases (90%). Extent of vascular involvement at time of locoregional failure included vasculature that had not been involved at diagnosis in 13 cases (42%). The pre-operative radiation plan that had been utilized provided a median V33 Gy and V25 Gy of the TV of only 53% (IQR: 34-72%) and 70% (IQR: 48-85%), respectively.

Conclusion

The TV encompassed the vast majority of locoregional failures, but dosimetric coverage of the TV was poor when only targeting gross disease and the full circumference of involved vasculature. As such, the TV may better serve as a basis for CTV design in BRPC/LAPC patients undergoing neoadjuvant radiation.