Room: Karl Dean Ballroom A1
Purpose: New techniques of acceptance testing and commissioning (ATC) has been introduced for a new class of ring-gantry linac. The procedures relies heavily on MV portal images and automated analysis. The design of the machine and the display console differs from the conventional c-arm (Varian 2300EX/Trilogy) systems. We performed a risk assessment for implementing the new ATC procedures for the pre-commissioned system.
Methods: Instead of relying on the beam data provided for the pre-commissioned machine, additional measurements were performed to supplement the spot-checks recommended by the vendor. Five physicist, who were involved in the ATC of 3 machines (1 academic and 2 veterinary clinics), participated in the failure modes and effects analysis (FMEA). Potential failure modes, causes of failure, and their impact were identified. A process map was generated and the probability of occurrence, severity, and detectability for each failure mode (FM) was scored to generate the risk priority number (RPN) following AAPM-TG100 guidelines.
Results: A total of 9 sub-processes (with 15 potential FMs) and 19 sub-processes (with 45 potential FMs) were identified for the acceptance and commissioning process respectively. The top 3 failure modes for acceptance includes: error in absolute dose calibration (RPN = 118), machine temperature and water flow rate inconsistencies (RPN =112), and insufficient door clearance to fit the assembled machine (RPN=101). The top 3 FMs for commissioning includes: error in determining the non-isocentric SSD (e.g. SSD of 90cm) from lateral MV images (RPN =128), error in determining the SSD due to the dependence on the window setting of the image intensity (RPN =122), and the potential error for setting up unique calibration options recommended by the vendor.
Conclusion: Potential FMs and hazardous steps in the ATC process have been identified. This analysis will be invaluable in mitigating errors and ensuring that the ATC is completed correctly.
Risk, Calibration, Commissioning
TH- External beam- photons: Quality Assurance - Linear accelerator