TPS4167 Background: There is growing consensus for the use of neoadjuvant therapy in patients with potentially operable pancreatic adenocarcinoma (PC). However, there is not consensus on the type and duration of chemotherapy or radiation therapy (RT) dose. Stereotactic body radiation therapy (SBRT) has gained popularity despite the absence of prospective data for its use in the preoperative setting. Furthermore, SBRT preoperatively has not been standardized. At present, there exists no randomized data comparing preoperative SBRT with conventionally fractionated concurrent chemo-RT. We designed this trial to examine differences between pre-op RT dose and fractionation schedules. Methods: This study is a prospective, randomized, two-arm, phase II clinical trial. Eligible patients must have cytologically confirmed PC and be deemed suitable for surgical resection with resectable, borderline resectable, or locally advanced type A disease, based on cross-sectional imaging. Before randomization patients are stratified by clinical node positivity, neoadjuvant chemotherapy, and stage of disease. Patients are then randomized to either 50.4 Gy over 28 fractions with concurrent weekly Gemcitabine vs SBRT to a total dose of 25-35 Gy over 5 fractions. The primary endpoint of the study is pathologic node positivity. We hypothesize that patients treated with neoadjuvant chemotherapy followed by conventionally fractionated chemo-RT will have a lower rate of pathologic node positivity as compared to those patients treated with neoadjuvant chemotherapy followed by SBRT. Secondary endpoints include patient reported quality of life, local recurrence, primary tumor pathologic response, margin status, surgical complications, MR based treatment response, and overall survival. We anticipate a node positivity rate of 37% when using preoperative chemotherapy followed by SBRT. We hypothesize that treatment with chemotherapy followed by conventionally fractionated chemo-RT will reduce the rate of node positivity to 17%. Using a one-sided Type I error rate of 0.1, approximately 88 total patients (44 per arm) provide an 80% power to detect the hypothesized difference in pathologic node positivity between the two arms. To address patient dropout, an additional 14 patients (about 15%) will be enrolled for a total target accrual of 102 patients. The trial opened in November 2018 and 8 of the planned 102 patients have been enrolled. Clinical trial information: NCT03704662.
MBCL-41. TREATMENT FAILURE PATTERNS ACROSS MEDULLOBLASTOMA SUBGROUPS WITHIN A PROSPECTIVE PHASE II CLINICAL TRIAL OF RISK-ADAPTED, VOLUME-REDUCED RADIATION THERAPY AND DOSE-INTENSE CHEMOTHERAPY WITH STEM CELL SUPPORT