Pancreatic Stereotactic Body Radiation Therapy With or Without Hypofractionated Elective Nodal Irradiation

Abstract

Pancreatic stereotactic body radiation therapy (SBRT) is limited to gross tumor without elective coverage for subclinical disease. Given a better understanding of recurrence patterns, we hypothesized that the addition of elective nodal irradiation (ENI) to pancreatic SBRT would be tolerable and would decrease locoregional progression. We conducted a retrospective 1:2 propensity-matched cohort study to compare toxicity and locoregional progression among patients treated with pancreatic SBRT with or without ENI. In the SBRT+ENI cohort, an elective target volume was delineated per Radiation Therapy Oncology Group guidelines and treated to 25 Gy in 5 fractions alongside 40 Gy in 5 fractions to gross disease. The primary outcome was the cumulative incidence of locoregional progression, with death as a competing risk. Among 135 candidate controls treated with SBRT alone, 100 were propensity-matched to 50 patients treated with SBRT+ENI. All patients completed SBRT. Median potential radiographic follow-up was 28 months. The incidence of late and serious acute toxicity was similar between matched cohorts. However, SBRT+ENI was associated with a statistically significant increase in acute grade 1 to 2 nausea (60% vs 20%, P < .001). The 24-month cumulative incidences of locoregional progression with and without ENI were 22.6% (95% confidence interval [CI], 10.0%-35.1%) versus 44.6% (95% CI, 34.8%-54.4%; multivariable-adjusted hazard ratio, 0.39; 95% CI, 0.18-0.87; P = .021). This was stable in sensitivity analyses of uniform prescription dose, multiagent chemotherapy, and resectability. There were fewer peripancreatic (0% vs 7%), porta hepatis (2% vs 7%), and peri-aortic/aortocaval (5% vs 12%) recurrences after SBRT+ENI, but no difference in survival. Pancreatic SBRT+ENI was tolerable and did not increase late or serious acute toxicity relative to a matched cohort undergoing SBRT alone, but did increase acute grade 1 to 2 nausea. The addition of ENI to SBRT was associated with decreased locoregional progression but not improved survival. Further studies are warranted to determine whether ENI offers meaningful benefit.