[Safety Analysis Using Event Tree Analysis for Multi-Ion Therapy].

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Science

Context:

• National Institutes for Quantum Science and Technology (QST) is developing multi-ion therapy for enhanced biological effects in charged particle therapy.
• A new treatment system was developed at the Heavy Ion Medical Accelerator in Chiba (HIMAC) to enable clinical feasibility of multi-ion therapy, allowing for changes in ion species during irradiation.

Purpose:

• To conduct a safety analysis of the new multi-ion therapy treatment system, focusing on newly introduced processes in treatment planning, accelerator, and irradiation.
• To verify the sufficiency of multiple safety barriers, including interlock systems and human checks, against potential malfunctions and human errors.
• To identify critical initial events with a high probability of leading to serious accidents.

Summary:

• Event Tree Analysis (ETA) was applied to a novel multi-ion therapy system at QST, analyzing safety barriers in treatment planning, accelerator, and irradiation processes.
• The analysis identified 35 initial events, with 5 flagged as cautionary due to a high probability (>10^-4) of leading to serious accidents, indicating insufficient safety barriers.
• System malfunctions and human errors that could cause serious accidents were clarified, and the effectiveness of existing safety measures was systematically evaluated.

Impact:

• The study successfully identified critical safety vulnerabilities in the multi-ion therapy system, guiding necessary improvements before clinical trials.
• The developed safety analysis procedure using ETA provides a robust framework for future radiotherapy system development at QST and other institutions.
• Findings will inform enhancements to safety barriers for the five identified cautionary initial events, ensuring enhanced patient safety in advanced cancer treatment.