Author: Ila Farhang, Ryan D. Foster, Devin Heitz, Jordan B Lunsford, Ashkan Shafiee 👨🔬
Affiliation: Atrium Health Wake Forest Baptist, Atrium Health/LCI Cabarrus 🌍
Purpose: American Association of Physicists in Medicine (AAPM) Task Group (TG) -51 is a widely utilized protocol for the absolute calibration of linear accelerators. The purpose of this project was for medical physics residents to perform a TG-100 risk assessment for the TG-51 process. The project provided a valuable learning experience in practicing the implementation of TG-100, review of the TG-51 processes and resulted in a resource that can be used by future trainees.
Methods: Residents developed a process map detailing the steps required to perform TG-51. The process map was divided into four main process steps: gathering equipment, setup, scanning, and output measurements. A Failure Modes and Effects Analysis (FMEA) and Fault Tree Analysis (FTA) were also completed. Potential failure modes and effects were identified for each process step and scored for severity. Causes associated with each failure mode were scored for occurrence and detectability. The FTA was completed for the highest scoring risk priority number (RPN) steps.
Results: The process map had a total of 39 steps and 21 failure modes were identified. Each failure mode had multiple causes resulting in 84 failure mode/cause pairs. The top three RPN scores were associated failure modes of incorrect measurement depth, use of an inappropriate chamber during output measurements, and omission of lead foil for flattening filter free beams. The FTA identified quality management steps to prevent or catch mistakes in the process.
Conclusion: Process-mapping for students and trainees proves to be a valuable tool for comprehension. Taking an FMEA approach to TG-51 highlights the most vulnerable steps in reference dosimetry, allowing physicists to proceed carefully when completing these steps. Trainees can then use FTA reasoning to best mitigate or avoid these errors when completing TG-51.