Comprehensive Analysis of Data From a Nationwide Japanese Cohort on Particle Therapy for Metastatic Liver Tumors.

[PURPOSE] This study evaluated the efficacy and safety of particle therapy (PT) for treating metastatic liver tumors. Conducted by the Japanese Society for Radiation Oncology, this nationwide, multi-institutional analysis examined PT outcomes, including overall survival (OS) rates and adverse events, to determine its potential as a treatment option for patients with limited liver metastases.

[METHODS AND MATERIALS] This nationwide, multi-institutional prospective cohort included patients treated with proton beam therapy and carbon-ion radiation therapy between 2016 and 2019. This is a retrospective cohort study utilizing registry data of metastatic liver tumors. PT dose schedules used varied based on tumor location. Outcomes assessed included OS, progression-free survival (PFS), local control (LC), and late treatment-related toxicities of grade ≥3.

[RESULTS] Among 322 eligible patients, the 2- and 5-year estimated OS rates were 55.7% and 32.8%, respectively, with a median survival time (MST) of 28.6 months. Patients with single lesions, particularly those with colorectal or breast cancer, demonstrated higher survival rates than those with multiple lesions. Patients with smaller tumors (<5 cm), especially in colorectal, pancreatic, gastric, and esophageal cancers, also showed improved survival compared with those with tumors ≥5 cm. Cox proportional hazards model analysis showed significant difference in maximal tumor diameter in colorectal cancer and pancreatic cancer (both P = .002) and number of lesions in breast cancer (P = .02). In a condition-specific subgroup analysis, MST exceeded 5 years in patients with breast cancer who had a single lesion or who did not receive concurrent systemic therapy. The 2- and estimated 5-year PFS rates were 23.5% and 12.8%, respectively, with MST of 9 months. The 2- and estimated 5-year LC rates were 74.3% and 66.4%, respectively. Recurrence was observed in 223 patients (local only, 43; distant only, 163; both, 17). Adverse events occurred in 3.1% of patients, primarily dermatitis and hepatobiliary disorders, with no grade 5 toxicities observed.

[CONCLUSIONS] PT is expected to provide excellent LC and low rates of serious adverse events for metastatic liver tumors. Promising OS rates, particularly in cases of colorectal and breast cancer, suggest that PT offers a survival advantage to carefully selected patients.