3108 - The Japanese Nationwide Prospective Cohort Data of Proton Beam Therapy for Liver Oligometastasis in Pancreatic Cancer Patients

H. Yamaguchi¹, N. Fukumitsu², H. Numajiri³, and H. Ogino⁴; ¹Department of Radiation Oncology, The James Cancer Center, Ohio State University Wexner Medical Center, Columbus, OH, ²Kobe Proton Center, Kobe, Japan, ³Departement of Radiation Oncology and Proton Medical Research Center, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan, ⁴Department of Radiation Oncology, Nagoya Proton Therapy Center, Nagoya, Japan

Purpose/Objective(s): A nationwide multicenter prospective cohort study on particle therapy was launched by the Japanese Society for Radiation Oncology (JASTRO). We analyzed the outcome of proton beam therapy (PBT) for liver oligometastasis in pancreatic cancer patients. Materials/

Methods: Cases in which PBT was performed at all Japanese facilities between 2016 and 2019 were enrolled. The patients were selected based on the following criteria: the primary cancer was controlled, liver recurrence without extrahepatic tumors, and no more than three liver lesions. The dose and fraction of PBT were used in the unified treatment policy established by JASTRO. The local control (LC), overall survival (OS), and progression free survival (PFS) rates were calculated using the Kaplan-Meier method. Factors possibly related to OS, such as patient`s age, performance status (PS), size and number of liver tumors, and history or refractory of chemotherapy were investigated. The cut-off values were estimated using the receiver operating characteristic curve and area under the curve at the 12 months mortality event. Univariate analysis was performed using the log-rank test. Regarding the safety outcomes, adverse events (AEs) were investigated.
Results: Fifteen males and nine females, with a median age of 64 (range, 40–82) years were enrolled. PS 0/1/2 was 11/11/2 patients, respectively. A total of forty lesions were included. PBT was selected because one patient refused liver resection even though it was resectable disease, twenty-one patients had unresectable liver metastasis, and two patients were unknown. Fifteen patients had refractory chemotherapy. Seven patients had concurrent chemotherapy with PBT. The median maximal diameter tumor size in each patient, fraction size, and biological effective dose using the linear-quadratic model with a/ß = 10 Gy ((BED)₁₀) were 31 (13–170) mm, 6.6 (2-8) Gy (relative biological effectiveness)/fraction, and 109.6 (88.8-115.2) Gy, respectively. Statically calculations were performed on 19 patients because 5 patients were missing post-PBT data. The median follow-up period was 7.9 (0.3-32.4) months. Two patients were alive at the end of observation period. The 1-, 2-year LC rates of liver metastasis after PBT were 53.3, 40.0%, respectively, median LC time was 12.4 months. The 1-, 2-year OS rates were 47.7, 17.8%, respectively, and median OS time was 11.4 months. The 1-, 2-year PFS rates were 5.3, 0%, respectively, and median PFS time was 4.4 months. The tumor size was the only significant OS related factor (p = 0.013). All patients completed PBT without interruption. Two patients had Grade 3 radiation induced dermatitis. No patients experienced other AEs.
Conclusion: Our prospective results, although based on a small number of patients, show that smaller than 34mm pancreatic liver metastasis patients may have been expected MST after PBT for around 14 months.