A novel audit methodology to improve detection of planning and delivery errors in passive motion management.

Background and purpose: End-to-end dosimetry audits, including respiratory motion, typically compare film measurements acquired in a moving frame directly to planned dose distributions that do not resolve the applied motion. Inherent motion-induced dose differences cannot be distinguished from error-induced differences in this analysis. An alternate comparison approach is proposed utilising both motion-coupled and decoupled film measurements to overcome the motion-induced differences, and improve error detection. Materials and methods: Reference internal target volume-based plans were created for lung and liver SBRT treatment sites in the ACDS motion phantom. A series of planning and delivery errors were introduced, and 4D dose accumulation was used to estimate the delivered dose. All plans were delivered to the phantom loaded with two films, analysed using gamma criteria ranging from 3%/1mm to 7%/5mm. A receiver operator characteristic decision matrix based on the gamma passing rate and 4D dose difference to reference ( Results: 7/13 introduced errors had Conclusions: Film measurements acquired in a moving frame are over-sensitive with low specificity. Eliminating the impact of motion using the proposed measurement/analysis approach enables more stringent gamma criteria (4%/2mm versus 5%/3mm) for better classification accuracy.