Patient-specific quality assurance and plan complexity: from photon standardisation to the unique characteristics of particle therapy

Maxence Rayer, Daniel Maneval, Cyril Moignier, Thomas Tessonnier, D. Lebhertz, Anthony Vela, Gary Delattre, Laetitia Lechippey, A. Batalla, Aurélien Corroyer‐Dulmont

Patient-specific quality assurance (PSQA) is a safety barrier ensuring that treatment plans calculated by the Treatment Planning System (TPS) are accurately delivered by the machine. With the widespread adoption of highly modulated techniques, such as Intensity Modulated Radiation Therapy (IMRT), Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Proton Therapy (IMPT) delivered via Pencil Beam Scanning (PBS), the sensitivity of delivery to plan complexity has increased drastically. Currently, the “gold standard” remains experimental PSQA, relying on pre-treatment measurements evaluated through dose comparison metrics, most commonly gamma index analysis. However, this approach is resource-intensive, its correlation with clinically relevant dose errors has been questioned, and applying spatial criteria (Distance-To-Agreement) loses its traditional experimental rationale when comparing purely computational dose distributions (e.g., TPS vs. Monte Carlo). In photon therapy, the field is shifting toward predictive quality assurance based on complexity indices, but this predictive framework is largely absent in particle therapy. Although Monte Carlo simulations and log-file analysis provide detailed data, translating this raw data into standardised complexity indices remains challenging and limits the use of artificial intelligence to predict delivery accuracy for proton and heavy ion therapy despite attempts. This narrative mini-review focuses primarily on research published between 2020 and 2025. We examine: (1) photon therapy as the benchmark for complexity-based prediction; (2) computational proton PSQA, which offers robust verification but currently lacks the complexity indices required for prediction; and (3) the extension to Ion Beam Therapy, arguing for the need to couple physical modulation with radiobiological effectiveness.