Japanese Nationwide Prospective Data of Proton Therapy for Liver Metastasis From Pancreatic Cancer

Evidence for the efficacy of proton beam therapy (PBT) for liver metastases of pancreatic cancer remains unclear. Therefore, we analyzed outcomes using data from a multicenter prospective study on particle therapy (PT) by the Japanese Society for Radiation Oncology (JASTRO).

We enrolled patients who underwent PBT at all facilities in Japan between 2016 and 2019. Patient selection criteria included liver recurrence without recurrence at the primary pancreatic tumor site after curative treatment, no other metastatic tumors in other organs, and up to three liver lesions. Moreover, inoperability and refractoriness to chemotherapy were part of the treatment eligibility criteria. The PBT dose and fractionation corresponded to the JASTRO treatment policy. The local recurrence (LR), overall survival (OS), and progression-free survival (PFS) rates were calculated using the Kaplan-Meier method. Factors potentially associated with LR and OS were analyzed. Adverse events (AEs) were also investigated. Twenty-four patients with a median age of 64 years (range, 40-82 years) and 40 lesions were enrolled in the study. The median tumor size was 11.7 (0.74-901.2 mL). Seven patients underwent concurrent chemotherapy; meanwhile, the median biological effective dose was 109.6 (range, 88.8-115.2) Gy.

The median follow-up period was 9.2 (range, 2.1-41.4) months. The 1-year LR rate was 16.7%. The 1-year OS and PFS rates were 37.5% and 4.2%, respectively, with median survival times of 9.3 and 4.7 months. However, no factors were related to LR. In multivariate analysis, levels of anti-carbohydrate determinant 19-9 (P < .01) and PFS duration after PBT (P < .01) were identified as statistically significant factors influencing OS. The only AE noted was radiation-induced dermatitis in 2 patients.

PBT was safe with few AEs, and patients likely to achieve long-term survival could be identified under appropriate conditions.