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Updated: May 2, 2026
Dynamic Lung Tumor Tracking for Stereotactic Ablative Body Radiation Therapy
Published on: June 7, 2015
Systems-theoretic process analysis of a CT-guided online adaptive radiation therapy system in a multi-vendor
Colleen Foote1, David M McClatchy1,2, Susu Yan1,2
1Division of Radiation Biophysics, Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts, USA.
Background:
Online adaptive radiation therapy (ART) is a relatively new process, and it is recommended that institutions starting an online ART program conduct a risk analysis to identify potential hazards. While Failure Modes and Effects Analysis (FMEA) is common, Systems-Theoretic Process Analysis (STPA) has also been used to evaluate online ART workflows.
Purpose:
An STPA hazard analysis was performed for a CT-guided online ART system in a multi-vendor environment. The goal was to identify potential risks and mitigations to guide the development of adaptive workflows and the quality management (QM) program.
Methods:
The STPA hazard analysis was performed in four steps. First, process maps for online ART were generated to describe the interactions between users and systems. In the second step, the process maps were refined to a single control structure diagram model. In the third step, potential unsafe control actions (UCAs) were enumerated by the physicists involved in the analysis. Finally, mitigation strategies to address the UCAs were identified.
Results:
A total of 496 UCAs were identified for 119 control actions, of which 239 (48.2%) were prioritized for mitigation due to having low or medium levels of detectability. The most frequent causal scenarios were accidental omission (20.1%), rushing (17.2%), and lack of training (15.9%). The most common consequences were delays (26.8%) and having to repeat work (13.5%). The two mitigation strategies considered to address the most causal scenarios were requiring trained adaptive staff (28.9%) and having physics oversight (19.9%).
Conclusions:
The STPA led to valuable insights into the potential causes of unsafe control actions and various mitigation strategies that were used to develop the QM program. Notably, most UCAs were attributable to interactions between users and the system, rather than system failures. It is recommended that every institution starting an online ART program perform a risk assessment for their environment.
