Using a Systems Engineering Approach to Design a Quality Management Program for Real-Time Marker-Less Lung Tumor Tracking
Abstract
Purpose
While real-time tracking devices have demonstrated benefits in clinical outcomes, their safe and effective implementation requires careful consideration. With errors more likely to result from system-wide flaws than isolated failures a systems engineering-based approach to implementation may be beneficial. In this work we apply the systems engineering-based approach system theoretic process analysis (STPA) to assess a real-time marker-less lung tumor tracking (MLTT) system and design a quality management program for safe implementation.
Methods
The MLTT application, developed for a clinical trial (NCT04086082) uses kV images and a patient specific model to identify the diaphragm and target using template matching. STPA was performed per guidelines, including the creation of a control structure diagram, unsafe control actions and causal scenarios. The resulting scenarios were categorized based on impact and/or potential cause which was used to indicate priority and frequency and/or timing. Next the mitigation requirements of each causal scenario were assessed, compared and rationalized based on similarity to determine the minimum set of mitigations.
Results
The STPA model of the MLTT system identified 40 unsafe control actions and 212 causal scenarios. The scenarios were divided into nine categories, including downstream, upstream, human-based, procedure-based and software malfunction. Seventeen mitigations were identified as covering most causal scenarios. Example recommendations include training and procedure development based on ‘work-as-done’ completed prior to introduction of the system and reviewed annually or on process changes. Practical validation that the system meets specification performed at commissioning, on update of the application and following changes in the system. Checks of patient specific files and plan components confirmed prior to fraction one.
Conclusion
STPA was applied to a MLTT system, with the outcomes used to design a quality management program. The QM program for the MLTT system will be evaluated in concert with the prospective clinical trial Real-time IGRT (NCT06708221).