Patterns of Local Failure After Stereotactic Body Radiation Therapy and Sequential Chemotherapy as Initial Treatment for Pancreatic Cancer: Implications of Target Volume Design

Abstract

Purpose: To identify patterns of local failure in patients with pancreatic cancer receiving stereotactic body radiation therapy plus chemotherapy as initial treatment, for the optimal design of target volumes encompassing a majority of local recurrences.

Methods and materials: Consecutive patients with resectable or borderline resectable but medically inoperable cancer owing to comorbidities and locally advanced pancreatic cancer undergoing stereotactic body radiation therapy and chemotherapy were reviewed. Local recurrences were plotted with respect to the celiac trunk (CT), superior mesenteric artery (SMA), and splenic artery on 1 computed tomographic scan of a template patient.

Results: Five hundred and ten patients were included. Median follow-up of the entire group was 21.8 months (range, 3.1-54.9 months). Two hundred and seventeen patients had locoregional recurrences, whereas local and distant progressions were found in 293 patients. One hundred and sixty-nine (33.2%) and 144 (28.2%) patients had recurrences closer to the CT and SMA, respectively, whereas both invasions of the CT and SMA were found in 115 patients (22.5%). In addition, 33 patients (6.5%) and 49 patients (9.6%) had recurrences at the hepatic hilum and the splenic artery, respectively. Besides these patterns of failure, 138 patients (27.1%) also experienced retroperitoneal progressions. The mean distance to the CT, SMA, and retroperitoneal recurrence was 9.0, 8.3, and 11.7 mm, respectively. Multivariable analysis demonstrated that advanced pancreatic cancer, recurrences at both the CT and SMA and the hepatic hilum, CA19-9 nonresponders, and BED₁₀ <60 Gy were predictive of worse survival.

Conclusions: Areas closer to the CT, SMA, and retroperitoneal space were at a high risk of local recurrences. Nonuniform and sufficient expansions from the gross tumor volume might be necessary, and the splenic vessels abutting the tumor might also be included in the target volume without compromise of dose constraints of organs at risk. In addition, at least BED₁₀ ≥60 Gy might be required to achieve better outcomes.