Gastrointestinal Cancer

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SU_16_2164 - Patterns of Failure Following Neoadjuvant SBRT or Fractionated Chemoradiation in Resectable and Borderline Resectable Pancreatic Cancer

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Patterns of Failure Following Neoadjuvant SBRT or Fractionated Chemoradiation in Resectable and Borderline Resectable Pancreatic Cancer
M. Barrord1, M. L. Mierzwa2, S. Ahmad3, O. Olowokure4, J. Sussman3, H. R. Esslinger5, T. Latif4, A. Gupta4, M. Smith1, S. Poreddy1, and J. R. Kharofa Jr6; 1University of Cincinnati, Cincinnati, OH, 2Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, 3University of Cincinnati Division of Surgical Oncology, Cincinnati, OH, 4University of Cincinnati Division of Hematology& Oncology, Cincinnati, OH, 5The Barrett Cancer Center, Cincinnati, OH, 6University of Cincinnati Department of Radiation Oncology, Cincinnati, OH

Purpose/Objective(s): SBRT during neoadjuvant therapy in resectable and borderline resectable (BLR) pancreas cancer (PCa) involves smaller target volumes and condensed fractionation relative to chemoradiation (FxChemoRT). However, no randomized trials have compared SBRT to FxChemoRT to assess differences in downstaging, patterns of failure, or survival outcomes.

Materials/Methods: All patients with BLR or resectable PCa cancer undergoing neoadjuvant therapy from 10/2012-7/2017 were retrospectively reviewed. Twenty-two patients were treated with FxChemRT which is the institutional standard. A subset of patients (n=18) were treated with SBRT on a prospective trial from 11/2014-7/2017. The FxChemoRT group received 50.4 Gy (28 fractions) to a customized CTV including the primary tumor, SMA, and celiac axis (5-10 mm PTV) using sensitizing gemcitabine or capecitabine. SBRT was delivered to the primary mass and abutting vessel with fiducials/abdominal compression to 33 Gy (5 fractions, 3 mm PTV). An optional elective CTV including the nodal space and mesenteric vessels was treated to 25 Gy. All patients were treated with 4 months of gemcitabine/abraxane or FOLFIRINOX prior to RT (table). Patients without disease progression at re-staging underwent resection. The cumulative incidence of local failure (LF), PFS, and OS were compared using a log rank test. The cumulative incidence of LF was defined as recurrence within conventional RT fields from the time of resection to LF or last CT without local disease.

Results: In the SBRT and FxChemoRT groups, there was no difference in resectable tumors (17% vs 32%, p=0.4), arterial abutment (83% vs 68%, p=0.5), or venous encasement (53% vs 36%, p=0.5). Resection was performed in 12 (57%) patients treated with FxChemoRT and 12 (67%) treated with SBRT (p=0.1). There was no difference in R0 rates in the SBRT or FxChemoRT groups [92% (11/12) vs 83% (10/12), p=0.1] or lymph node involvement [33% (4/12) vs 25% (3/12) p=0.6]. The PFS in patients treated with SBRT compared to FxChemoRT at 2 years was 7% vs 33% (p=0.04) for all patients and 11% vs 53% (p=0.01) in resected patients. At first progression, LF occurred in 0%(0/5) of FxChemoRT patients compared to 56%(5/9) of SBRT patients (table). LF rates at 1 year and 2 years from surgery in the SBRT vs FxChemoRT groups was (56% vs 20%) and (85% vs 20%) (p=0.01). The 2-year OS in the SBRT vs FxChemoRT groups was (46% vs 43%) (p=0.59) for all patients and (63% vs 58%) (p=0.83) in resected patients.

Conclusion: Patients treated with neoadjuvant SBRT had shorter PFS, more local only failures within conventional RT volumes, and less durable local control relative to FxChemoRT. Omission of elective vascular target volumes may result in unacceptable local recurrence patterns for patients undergoing curative resection.
SBRT FxChemoRT
N=18 % N=22 % P-value
Gem/nab-paclitaxel 13 72% 14 64% 0.57
FOLFIRINOX 5 28% 8 36%
Site of 1st Failure after Resection N=9/12 N=5/12
Distant 4 44% 5 100%
Local only 4 44% 0 0%
Local & distant 1 15% 0 0%

Author Disclosure: M. Barrord: None. M.L. Mierzwa: None. S. Ahmad: None. H.R. Esslinger: None.

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