COMPARISON OF SHORT-TERM ONCOLOGIC OUTCOMES FOR STEREOTACTIC BODY VERSUS CONVENTIONALLY FRACTIONATED RADIATION THERAPY IN RESECTED PANCREATIC ADENOCARCINOMA
Benjamin Powers*, Jessica Frakes, Pamela J. Hodul, Dae Kim, Daniel Anaya, Mokenge P. Malafa, Sarah Hoffe, Jason Fleming, Jason W. Denbo
Gastrointestinal Oncology, H. Lee Moffitt Cancer Center, Tampa, FL
Background: Neoadjuvant therapy (NAT) is commonly utilized in resectable and borderline-resectable pancreatic adenocarcinoma (PDAC). Radiation therapy is often incorporated into NAT regimens to increase the rate of margin negative resections, improve nodal downstaging, and allow for selection of patients with more favorable tumor biology. Stereotactic body radiation therapy (SBRT) has several benefits over conventionally fractionated radiation therapy (CFRT), which include higher doses per fraction, shorter duration of treatment, and ease of incorporation into systemic therapy regimens. Most reports of SBRT as a component of NAT for PDAC are from single institutions and uncommonly compare outcomes to CFRT.
Methods:The NCDB was used to identify clinical stage T1-T3 PDAC patients treated with NAT (radiotherapy +/- chemotherapy) who then underwent curative-intent surgical resection between 2008-2016. We evaluated the impact of SBRT (≥20Gy & ≥4Gy/fraction) compared to CFRT (≥45Gy & ≤2Gy/fraction) on margin status and lymph node disease burden, including the lymph-node ratio (LNR) (positive lymph nodes/lymph nodes examined). Statistical tests included Chi-square, Wilcoxon-Mann-Whitney U, and multivariable logistic regression.
Results:1,910 patients met inclusion and exclusion criteria of whom 229 (12.0%) received SBRT. In univariate analysis, factors associated with the SBRT group were race, insurance status, facility type, facility volume, and clinical T stage. (Table 1) Clinical N stage groups were similar and nearly all patients (97%) received chemotherapy. The pathologic T stage and R0 resection rates (92.6% SBRT vs 91.4% RT, p=0.614) were similar between groups. SBRT was associated with a higher pathologic N stage (p=0.006). After adjusting for potential confounders, SBRT was not a driver of R1 margin status (OR, 1.11; 95% CI 0.55-2.67). However, in the multivariable LNR ≥0.15 model, SBRT was associated with increased odds of LNR ≥0.15 (OR, 1.69; 95% CI 1.02-2.81). In the multivariable models, advancing pathologic T stage was associated with increased odds of R1 margin and LNR ≥0.15, and neoadjuvant chemotherapy was associated with decreased odds of R1 margin and LNR ≥0.15.
Conclusion: In resected PDAC treated with radiotherapy as a component of NAT, pathologic T stage, receipt of neoadjuvant chemotherapy, and SBRT were independently associated with short-term oncologic outcomes. When compared to conventionally fractionated radiotherapy, SBRT was associated with more extensive residual pathologic nodal disease (LNR ≥0.15), potentially a surrogate marker of locoregional control and/or survival. Further investigations into the short and long-term oncologic outcomes of SBRT in NAT regimens for PDAC are warranted prior to widespread adoption and implementation.
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