Log file-based 4D proton dose reconstruction for interplay assessment in clinical routine and simulation studies

We have implemented the reconstruction of interplay-affected dose distributions from the log files of the dynamic PBS proton beam delivery and of the breathing-induced intra-fractional motion. For the first time, such an algorithm is capable to consider amplitude-sorted 4DCT phases. We have validated the reconstruction accuracy by phantom experiments for several motion patterns and magnitudes. The module is applied in combination with weekly repeat 4DCTs to routinely monitor the PBS treatments of NSCLC patients in our clinic department. Further use cases are occasional pre-treatment interplay estimations and the interplay effect evaluations within a plan comparison study investigating the benefit of 4D robustly optimized proton plans for NSCLC patients with large breathing motion (>5mm).