Patterns of failure in a phase II trial of neoadjuvant chemotherapy and stereotactic body radiation therapy (SBRT) for resectable and borderline resectable (BLR) pancreatic cancer.

Abstract

482 Background: There is emerging interest in the role of SBRT in locally advanced pancreas cancer, however little prospective data exists examining the safety, efficacy, and optimal target volumes for SBRT in the neoadjuvant setting for resectable or BLR pancreatic cancer. Methods: Eighteen patients were enrolled from 11/2014-6/2017. SBRT was delivered to the tumor and abutting vessel with fiducials/compression and a 3 mm PTV margin to 33 Gy (6.6 Gyx5fxn) with an optional elective PTV to 25 Gy (5 Gyx5fxn) customized to the nodal space and mesenteric vessels. Patients without progression underwent surgery 4-6 weeks following SBRT. The primary endpoint is ≥ Grade 3 acute and late GI toxicity. Secondary endpoints included overall survival (OS), progression-free survival (PFS),and cumulative incidence of local failure (LF). LF is defined as recurrence within conventional RT volumes from the time of resection to local failure or last CT with no progression. Local failures were fused to planning CTs for dose quantification. Results: Thirteen patients had BLR tumors due to arterial abutment (n = 7) or SMV encasement (n = 8); 3 patients had resectable tumors. All patients received 4 months of gemcitabine/nab-paclitaxel (n = 13) or FOLFIRNOX (n = 5) prior to SBRT. There were no ≥ Grade 3 acute or late GI events. Metastases were noted in 6 patients (33%) at restaging or surgery. Surgery was performed in 12 patients (67%) with 11 (92%) R0 resections. Median OS and PFS are 21 months and 11 months, respectively. Progression occurred in 67% (8/12) of resected patients with first site of failure as distant (n = 3, 38%), local only (n = 4, 50%), and local and distant (n = 1,13%). The cumulative incidence of LF at 12 months from resection was 50%. All LF were outside to the PTV33 with median D90 of 11.5 Gy (4-25 Gy), V25 Gy of 51% (0-90%), and V33 Gy of 45% (0-52%). Conclusions: SBRT as a component of neoadjuvant therapy was well tolerated. However, local failures were predominantly observed outside the PTV33 volume within conventional RT volumes. Therefore, the durability of local control after SBRT in the neoadjuvant setting relative to chemoradiation merits close examination. Clinical trial information: NCT02208024.