3048 - Stereotactic Body Radiation Following Prior Radiotherapy for Pancreatic Cancer: A Single Institution Experience

M. A. Mohammed¹, A. H. Zureikat², M. Lotze³, A. Paniccia², K. K. Lee², J. Shogan¹, A. A. Vera¹, B. Elgohari¹, M. K. Abdelhakiem¹, J. Y. Zhang⁴, S. A. Burton¹, and S. G. Ellsworth¹; ¹Department of Radiation Oncology, UPMC Hillman Cancer Center, Pittsburgh, PA, ²Department of Surgery, University of Pittsburgh, Pittsburgh, PA, ³University of Pittsburgh Hillman Cancer Center, Pittsburgh, PA, ⁴UPMC, Department of Hematology/Oncology, Pittsburgh, PA

Purpose/Objective(s): Pancreatic cancer is a common and lethal malignancy with an approximately 30% risk of local recurrence following radiotherapy. There is a paucity of data regarding reirradiation of upper abdominal cancers including pancreatic cancer. Here we present our data for patients who were treated with re-irradiation using stereotactic body radiotherapy (SBRT). Materials/

Methods: 37 patients were included in our analysis; median age was 64 years (range 47-83), and 17 patients (46%) were women. Median baseline KPS was 80. The majority of patients (n=26, 70%) underwent conventionally fractionated RT before SBRT (median BED10 = 59.4Gy) with the remaining 11 patients undergoing two courses of SBRT (median BED10 of SBRT course 1 = 79.2Gy). The median interval between 1st and 2nd RT courses was 10.0 mos (range 1.0-265.0 mos). Median PTV size for rSBRT was 23.2cc (range 7.6-312.7).
Results: 37 patients were included in our analysis; median age was 64 years (range 47-83), and 17 patients (46%) were women. Median baseline KPS was 80. The majority of patients (n=26, 70%) underwent conventionally fractionated RT before SBRT (median BED10 = 59.4Gy) with the remaining 11 patients undergoing two courses of SBRT (median BED10 of SBRT course 1 = 79.2Gy). The median interval between 1st and 2nd RT courses was 10.0 mos (range 1.0-265.0 mos). Median PTV size for rSBRT was 23.2cc (range 7.6-312.7). At the time of analysis, all patients had died, with a median OS from the end of SBRT of 9.7 mos (95%CI 6.4-12.9). Ten =grade 3 toxicities (27%) were attributed to RT, all of which were upper gastrointestinal (GI) bleeding. Median time to high-grade GI toxicity after rSBRT was 8 months; rates of =grade 3 toxicity were 2/11 (18%) in patients treated with 22-24 Gy x 1, 7/18 (39%) in patients treated with 9-12 Gy x 3, and 0/6 (0%) in patients treated with 5-8 Gy x 5, although these differences did not reach statistical significance. A trend (p=0.06) to lower risk of =grade 3 toxicity was also noted in patients who had undergone surgical resection (4/22 patients, 18%) vs those who had not (4/11 patients, 36%). No correlation between bleeding risk and interval between initial RT and rSBRT was noted.
Conclusion: We report an institutional series of SBRT-based reirradiation for pancreatic cancers. Although this approach was associated with an overall high-grade GI toxicity risk of 24%, risk of serious toxicity was numerically lower in lower-BED regimens as well as in patients who had previously undergone surgical resection of their tumor. rSBRT may be an option for selected patients with locally recurrent pancreatic cancer if conservative dosing regimens are followed.