Gastrointestinal Cancer

SS 38 - GI 4 - Hepato-Pancreatic-Biliary

277 - A Phase I/II Trial of Stereotactic Body Radiation Therapy for Unresectable Pancreatic Cancer Using Ablative (BED100) Doses

Wednesday, October 24
12:10 PM - 12:20 PM
Location: Room 206

A Phase I/II Trial of Stereotactic Body Radiation Therapy for Unresectable Pancreatic Cancer Using Ablative (BED100) Doses
L. Ni1, M. Kozloff2, T. Wu2, F. Arif2, M. Posner2, H. Kindler2, and S. Liauw3; 1Pritzker School of Medicine, University of Chicago, Chicago, IL, 2University of Chicago, Chicago, IL, 3The University of Chicago, Department of Radiation and Cellular Oncology, Chicago, IL

Purpose/Objective(s): The role of radiation therapy (RT) for unresectable pancreatic cancer is controversial. We explored the safety and efficacy of an aggressive 3-fraction regimen of stereotactic body RT (SBRT) in patients with unresectable disease.

Materials/Methods: This phase I/II trial included patients with biopsy proven unresectable or medically inoperable pancreatic cancer treated with any number of cycles of induction chemotherapy. The first 9 patients were accrued in a 3+3 design at 10, 12.5, and then 15 Gy x3, with subsequent patients treated at the maximally tolerated dose level. Treatment was delivered to gross tumor (median size 25 cc, delineated with MRI fusion) + 5-12 mm with image-guidance to fiducial markers and respiratory motion management. Normal tissue dose constraints were assigned priority over planning target volume (PTV) coverage, including max point dose to duodenum or stomach of 30 Gy. Chemotherapy was held 2 weeks prior to, and 4 weeks after SBRT. Dose limiting toxicity was defined as any grade 3+ toxicity within a 30-d window. Secondary endpoints included late toxicity, response to therapy, freedom from local failure (FFLF, RECIST criteria), and survival.

Results: 15 patients with T1-4N0 disease were enrolled (median age 61) after median 6 cycles of chemotherapy. The median pre-RT CA19-9 level was 108. In the dose-escalation cohort, there were no dose limiting toxicities, and subsequent patients were treated at 15 Gy x3. Median coverage of the gross tumor and planning target volume with the full prescription dose (V100%) were 95% and 80%, respectively. At a median follow-up of 12.8 mo, 13 patients have died. 30-d toxicity included 7 (47%) with grade 2 nausea and 1 (7%) with grade 2 diarrhea; there were no grade 3+ toxicities. All patients with elevated CA19-9 had a response (median nadir, 23). The median survival after SBRT was 12 mo (23 months after diagnosis) and median relapse free survival was 7 mo. At 1-year, FFLF was 80% (65% when incorporating clinical factors such as pain), and freedom from metastasis was 57%. Late grade 3+ GI toxicity was observed in 4 patients (25%, median 6 mo), including 1 associated death. Higher dose was not associated with local control (1-y FFLF 0% vs. 33% for dose ≤45 Gy vs. 45 Gy, p=0.07). Grade 3+ GI toxicity was associated with tumor volume (0% if <25 cc, 50% if >25 cc, p=0.01) and weakly associated with increasing dose to the duodenum (V26-30 Gy, p<0.2) and heterogeneity of dose within the PTV (V120%, p=0.07).

Conclusion: This aggressive (BED >100) SBRT regimen was associated with limited 30-d morbidity, a moderate degree of local control, and a risk for severe late GI toxicity that was more than minimal. Future use of this regimen could be restricted to patients with small volume tumors or those able to meet strict normal tissue constraints.

Author Disclosure: L. Ni: None. M. Kozloff: None. F. Arif: None. M. Posner: None. S. Liauw: None.

Stanley Liauw, MD

University of Chicago

Disclosure:
Employment
University of Chicago: Associate Professor: Employee

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