Monte Carlo simulations as the cornerstone of next-generation patient-specific quality assurance in particle therapy

Phantom-based Patient-Specific QA (PSQA) methods are resource-intensive and lack sensitivity, especially for Intensity Modulated Particle Therapy (IMPT) with steep dose gradients. To address these challenges, the European Particle Therapy Network (EPTN/ESTRO) has developed guidelines for phantom-less PSQA methods, including Monte Carlo (MC)-based Independent Dose Calculation (IDC) and log file-based QA. Although IDC can be standardized across clinics, the quality and availability of machine log files vary significantly by vendor, underscoring the need for manufacturers to standardize log file information and accessibility for the user community. Rapid Particle Therapy (PT) advancements (e.g. Linear Energy Transfer (LET) painting, Particle Arc Therapy (PAT), Multi-Ion Therapy (MIT), FLASH, Spatially Fractionated Radiation Therapy (SFRT), etc.) are reshaping established treatment paradigms. The future prescription may include not only dose, but also LET, dose rate, spatial dose modulation and biological information. Once treatment quality depends on quantities that cannot be measured in patient-specific phantoms, computational verification becomes unavoidable. To ensure the safe integration of these innovations, MC-based PSQA becomes essential, releasing machine and human resources, providing more time for patient treatment and substantially reducing the ecological impact of PSQA.