A Multi-Institutional Initiative on Patient-related Quality Assurance: Independent computational dose verification of fluence-modulated treatment techniques.

Purpose: This multi-institutional study investigates whether computational verification of fluence-modulated treatment plans using independent software with its own Strahlerkopfmodel is an appropriate method for patient-related quality assurance (PRQA) in the context of various combinations of linear accelerators (linacs), treatment techniques and treatment planning systems (TPS). Materials and methods: The PRQA-software's (Mobius3D) recalculations of 9 institutions' treatment plans were analyzed for a horseshoe-shaped planning target volume (PTV) inside a phantom. The recomputed dose distributions were compared to a) the dose distributions as calculated by all TPS's and b) the measured dose distributions, which were acquired using the same independent measuring system for all institutions. Furthermore, dose volume histograms were examined. The penumbra deviations and mean gamma values were quantified using Verisoft (PTW). Additionally workflow requirements for computational verification were discussed. Results: Mobius3D is compatible with all examined TPSs, treatment techniques and linacs. The mean PTV dose differences (Mobius3D-TPS, <3.0%) and 3D gamma passing rates (>95.0%) led to a positive plan acceptance result in all cases. These results are similar to the outcome of the dosimetric measurements with one exception. The mean gamma values (<0.5) show a good agreement between Mobius3D and the TPS dose distributions. Conclusion: Using Mobius3D was proven to be an appropriate computational PRQA method for the tested combinations of linacs, treatment techniques and TPS's. The clinical use of Mobius3D has to be complemented with regular dosimetric measurements and thorough linac and TPS QA. Mobius3D 's computational verification reduced measurement effort and personnel needs in comparison to dosimetric verifications.