UCSF

Background

We explored the safety and efficacy of ablative doses of stereotactic body radiation therapy (SBRT) for unresectable pancreatic cancer.

Methods

This phase I/II trial included patients with unresectable pancreatic cancer previously treated with any number of cycles of induction chemotherapy. Patients were enrolled according to a 3+3 dose escalation design at 10, 12.5, and 15 Gy ×3, with subsequent patients at the maximally tolerated dose (MTD). Treatment was delivered to gross tumor delineated with MRI fusion using image-guidance to fiducial markers. Dose-limiting toxicity (DLT) was defined as grade 3+ toxicity within 30 days. Secondary endpoints included late gastrointestinal (GI) toxicity, freedom from local failure (FFLF), and survival.

Results

Fifteen patients received a median 10 cycles of chemotherapy. There were no DLTs, and the MTD was 15 Gy ×3. Thirty-day toxicity included grade 2 nausea (46%) and grade 2 diarrhea (7%). Median survival after SBRT was 12.8 months (23 months after diagnosis) and median relapse-free survival was 7 months. At 1-year, FFLF was 80%. Four patients had grade 3+ GI bleeding after 30 days (median 6 months). Grade 3+ GI bleeding was associated with tumor volume (P=0.01), heterogeneity of dose within the planning target volume (PTV) (V120, P=0.03), and duodenal dose (V26-30 Gy, P<0.2).

Conclusions

This aggressive SBRT regimen demonstrated limited 30-day morbidity, a moderate degree of local control, and a moderate risk for late GI bleeding. Further work is necessary to define the most appropriate hypofractionated radiation therapy (RT) regimen in the ablative dose range.