Mitigating Risks in Cone Beam Computed Tomography Guided Online Adaptive Radiation Therapy: A Preventative Reference Planning Review Approach.

Purpose: Online adaptive radiation therapy (oART) treatment planning requires evaluating the temporal robustness of reference plans and anticipating the potential changes during treatment courses that may even lead to risks unique to the adaptive workflow. This study conducted a risk analysis of the cone beam computed tomography guided adaptive workflow and is the first to assess an adaptive-specific reference planning review that mitigates risk in the planning process to prevent events and treatment deficiencies during adaptation. Methods and Materials: A quality management team of medical physicists, residents, physicians, and radiation therapists performed a fault tree analysis and failure mode and effects analysis. Fault trees were created for under/overdosing targets and treatment deficiencies and assisted in identifying failure modes for the failure mode and effects analysis. Treatment deficiency was defined as a nonideal oART plan resulting in treatment with a lower quality plan (either oART or scheduled plan), treatment delay, or canceling treatment for the day. A reference planning checklist was created to catch failure modes before reaching the patient. Risk priority numbers (RPNs = severity * detectability * occurrence) were scored with and without the reference planning checklist to quantify risk mitigation. A root cause analysis was conducted for an event where an adaptive plan failed to generate. Results: The reference planning checklist (with items covering patient background, contouring/planning robustness for anatomy variability, and machine limitations) reduced the RPN for all failure modes. Only 1 failure mode with an RPN > 150 occurred with the reference planning checklist compared with 29 failure modes without, including 14 adaptive-specific failure modes. Contouring, planning, setup, scheduling, and documentation errors were identified during the fault tree analysis. Twenty-nine of 70 errors were adaptive-specific. The reference planning checklist could address 23 of 33 errors for over- or underdosing and 28 of 37 errors for treatment deficiency. The root cause analysis highlighted the need to check the setup prior to adaptive plan delivery and the time-out checklist. Conclusions: The reference planning checklist improved the detection of the failure modes and improved the quality and robustness of the plans produced for oART. It is ideally performed before the physician plan review to prevent last-minute replan (before or after first adaptive treatment) and delay of patient start. The checklist presented can be modified based on failures specific to individual clinics and used at various planning steps based on available resources.