Incidence and Patterns of Locoregional Failure After Stereotactic Body Radiation Therapy for Pancreatic Adenocarcinoma

Abstract

Purpose: Stereotactic body radiation therapy (SBRT) is increasingly utilized in the neoadjuvant and definitive settings for pancreatic adenocarcinoma. The risk of local and regional recurrence after this treatment remains largely unknown. Because of the lack of elective nodal treatment and high fractional dose, we hypothesized that the incidence of regional out-of-field recurrence would predominate after SBRT.

Methods and materials: Electronic medical records of all patients treated in our department with SBRT for pancreatic adenocarcinoma were retrospectively reviewed. Patients were separated into those who converted or did not convert to surgical resectability. Demographic, treatment, and outcome data were collected and analyzed. Recurrence was assessed based on the Response Evaluation Criteria In Solid Tumors version 1.1. Treatment plans were reviewed to determine the locations of failure with respect to treatment volume. Statistical comparisons were made using Mann-Whitney U testing for continuous variables and χ² testing for dichotomous variables.

Results: Data on 69 patients was available for analysis. After treatment, 18 patients (26.1%) suffered in-field recurrence and 11 patients (15.9%) recurred regionally out of field. The median time to in-field and out-of-field failures were similar at 120.5 and 108.0 days, respectively (P = .65). Of those who failed out-of-field, 4 of 11 patients (36.4%) were without in-field failure prior to death. In-field failure rates were less in patients who subsequently underwent surgical resection compared with those who did not (2 of 22 patients [9.1%] vs 16 of 47 patients [34.0%]; P = .028), but out-of-field recurrence was unaffected by subsequent surgical resection (3 of 22 patients [13.6%] vs 8 of 47 patients [17.0%]; P = .720). All out-of-field failures occurred in areas that received <2600 cGy.

Conclusions: The incidence of out-of-field failure remains acceptable after SBRT for pancreatic adenocarcinoma. Despite the high biological equivalent dose allowed by SBRT, in-field control remains problematic and continues to signal relative radiation resistance that is associated with bulky disease.