ESTRO 2024 - Abstract Book

S4923

Physics - Quality assurance and auditing

ESTRO 2024

Purpose/Objective:

Patient-specific quality assurance (PSQA) using measurements in a phantom is standard practice in many particle therapy centers. This method has received criticism for its limited sensitivity to various errors and for being labor intensive. With increased access to treatment log files and the increased accessibility of alternative dose calculation systems (especially Monte Carlo), many centers are considering discontinuation of some or all PSQA measurements and a transition to log file-based PSQA and/or secondary dose calculations. However, questions remain about the safety and effectiveness of these newer PSQA methods 1 . PTCOG’s Treatment Efficiency Subcommittee has evaluated the viability, benefits, and challenges of different PSQA methods, including the traditional measurement-based approach, the use of treatment delivery log files, and independent secondary dose calculations. The objective of this study is to provide guidance for the particle therapy community on the value of various PSQA approaches. The working group includes participants from several countries utilizing equipment from various vendors and following different treatment workflows. A risk assessment was performed using the Failure Modes and Effects Analysis (FMEA) formalism, following the recommendations of AAPM TG-100 2 . The roles of the oncology information system, treatment planning system, and delivery system were considered, as well as the communication between these systems. A generic, representative workflow plan was developed based on the processes in the participating particle therapy institutes, and failure modes were identified for each process step. The failure modes and their associated workflow steps that were considered likely to impact (positively or negatively) the various PSQA methods were selected for evaluation. Each failure mode was scored once assuming no PSQA-like mitigation was performed, forming a risk baseline. Each failure mode was then scored again assuming the use of measurement-based PSQA, log file-based PSQA, or independent secondary dose calculation. Each mitigation was scored in two parts - first assuming only the data transfer and plan manipulation steps took place, and second assuming the complete process, including measurement and analysis. The mean relative risk priority number (RPN) score differences were calculated for each PSQA approach, in order to provide a quantitative assessment of the risk mitigation potential of the respective PSQA techniques. Material/Methods:

Results:

The data transfer and plan manipulation steps contribute on average to a slight increase in risk for all three mitigations. This occurs most strongly for the measurement-based PSQA (7.8%), then for the Secondary Dose Calculation approach (5.0%) and least for the Log-file-based PSQA (0.1%). However, when considering the complete process, all mitigations lead to measurable risk mitigation. The log file-based PSQA shows the most significant reduction in risk with -39.2%, followed by the measurement-based approach with -31.8%. The secondary dose calculation contributes least to the risk reduction with -6.8%.