One Versus 3 Fraction Pancreatic SBRT for Pancreatic Adenocarcinoma: Single Institution Retrospective Review

Abstract

Early reports of Stereotactic Body Radiation Therapy (SBRT) for pancreatic carcinoma used a single fraction regimen, but subsequent clinical experience switched to multi-fraction regimens. We therefore conducted a single institution review of patients treated with single or multi-fraction SBRT to determine if there were differences in outcome based on fractionation. We conducted a retrospective review of patients treated between 2004 and 2014. Overall survival (OS), local control (LC), regional control (RC), and late toxicity were our primary endpoints. Statistical analysis was performed using IBM SPSS Statistics Version 23. P-values less than 0.05 were deemed significant for both univariate (UVA) and multivariate analysis (MVA). We identified 289 patients with 291 lesions who had pathologically confirmed pancreatic adenocarcinoma. Median age was 69 (33-90) years. Median gross tumor volume (GTV) was 12.3 cm3 (range 8.6-21.3) and planning tumor volume (PTV) 17.9 cm3 (range 12–27). Single fraction was used in 90 (30.9%) and multifraction in 201 (69.1%) lesions. At a median follow-up of 17.3 months (IQR 10.1-29.3 months), the median survival for the entire cohort 17.8 months with a 2-year OS of 35.3%. While univariate analysis showed multi-fraction schemes to have a higher 2-year OS 30.5% vs. 37.5% (P = 0.019), it did not hold significance on multivariate analysis. Multi-fractionation schemes were found to have a higher 2-year LC (69.7% vs 56.8%) on MVA [HR = 0.53, 95% CI (0.33-0.85), P = 0.009]. Fractionation scheme on univariate analysis did not affect regional control (P = 0.541) or distant metastasis (P = 0.226). At 2 years, late grade 2+ toxicity was 7.8% and late grade 3+ toxicity was 3.5%. Post-SBRT CA19-9 was found on MVA to be a prognostic factor for OS [HR = 1.01, 95% CI (1.01-1.01), P = 0.009], RC [HR = 1.01, 95% CI (1.01-1.01), P = 0.02] and DM [HR = 1.01, 95% CI (1.01-1.01), P = 0.001]. This single institution retrospective review shows multi-fraction regimens SBRT had a higher LC than single fractionation regimens. While multi-fraction regimens had a higher OS on univariate, this did not hold true on MVA. We showed low rates of late grade 2+ and grade 3+ toxicity with SBRT. Post-SBRT CA19-9 was found to be significant factor for OS, RC, and DM. This single institution report is the largest retrospective series showing multi-fraction regimens SBRT is associated with a higher LC than single fractionation regimens.