Gastrointestinal Cancer

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SU_19_2190 - Outcomes of Two 100 Gy BED Radiation Regimens for Inoperable Pancreas Cancer

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

Outcomes of Two 100 Gy BED Radiation Regimens for Inoperable Pancreas Cancer
P. J. Parikh1, M. C. Roach Jr1, O. L. Green1, R. Kashani2, S. Rudra3, L. E. Henke3, and J. R. Olsen4; 1Washington University School of Medicine, St. Louis, MO, 2University of Michigan, Ann Arbor, MI, 3Washington University School of Medicine, Department of Radiation Oncology, St. Louis, MO, 4Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, CO

Purpose/Objective(s): There is increasing interest in ablative doses (~100 Gy BED) of radiation for pancreatic cancer. There are two approaches for delivery: hypofractionation (HF) and high dose stereotactic body radiation therapy (SBRT). The goal of this study was to evaluate the outcomes of inoperable pancreatic cancer patients treated with both approaches using MR guided radiation therapy (MRgRT).

Materials/Methods: A total of 30 patients with locally advanced, borderline resectable or medically inoperable pancreatic cancer were diagnosed with pancreatic cancer from January 2015 to January 2017 and treated with ablative doses of MRgRT at a single institution. Hypofractionated radiation was given with a median prescription dose of 67.5 Gy / 15 fractions (range 50-67.5 Gy). All patients receiving hypofractionated radiation received concurrent chemotherapy, consisting of gemcitabine, gemcitabine and nab-paclitaxel,, capecitabine or 5FU. SBRT was given with a prescription dose of 50 Gy / 5 fractions, daily or every other day, without concurrent chemotherapy. MRgRT allowed daily creation of a new isotoxic plan, in which the plan would cover as much of the tumor each day while keeping 0.5 cc of the gastrointestinal (GI) organs at risk under 33-36 Gy for the SBRT patients and under 45-50 Gy for the HF patients. Overall survival (OS) was calculated from both date of diagnosis and start of radiation therapy until death or last follow up. Patients lost to follow-up with known recurrent or metastatic disease were marked as dead at time of last follow-up for this analysis to avoid positive bias. Kaplan Meier analyses were done to compare survival; Student’s t-test or Fischer’s exact test were used for comparisons of patient characteristics.

Results: 23 patients received HF radiation and 7 patients received SBRT. Median follow-up from diagnosis was 15.3 months and median follow-up from start of radiation was 10.8 months. Compared to HF patients, SBRT patients were older (average age 78 vs 62, p=.001) and were more likely to have medically inoperable disease rather than borderline resectable or locally advanced disease (3/7 vs 1/23; p=.02). OS from diagnosis at 15 months was 81% for SBRT patients and 72% for hypofractionated patents (p=NS); 1 year survival from start of radiation was 82% for the SBRT patients and 72% for HF patients (p=NS). One patient who received her SBRT inadvertently within 3 days of gemcitabine/nab-paclitaxel had a grade 4 duodenal ulcer. No other patients had grade ≥ 3 radiation related toxicity.

Conclusion: Patients treated with ablative doses of radiation using HF or SBRT, demonstrate excellent OS. Furthermore, toxicity with either technique is low. This work supports further investigation of ablative radiation to the pancreas. In particular, a randomized study between the two regimens is warranted.

Author Disclosure: P.J. Parikh: Research Grant; Varian Medical, Viewray. Honoraria; Viewray. Speaker's Bureau; Sirtex. Advisory Board; Sirtex. Stock; Holaira. M.C. Roach: Travel Expenses; BTG, Varian, Elekta. O.L. Green: Honoraria; ViewRay, Inc. Travel Expenses; ViewRay, Inc. R. Kashani: None. S. Rudra: None. L.E. Henke: Speaker's Bureau; Viewray. J.R. Olsen: Senior Associate Editor; International Journal of Radiation Oncology Biolog.

Parag Parikh, MD, BSE

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