Room: ePoster Forums
Purpose: To investigate if there is a correlation between the 2D gamma-passing rate (GPR) of VMAT plans measured by the Sun Nuclear ArcCheck system and the magnitude of differences in DVH parameters between the delivery and planning data.
Methods: We analyzed 21 VMAT plans for the treatment of head and neck cancer patients. The treatments used three non-coplanar arcs with the SIB (Simultaneous integrated Boost) technique and a 6 MV photon beam of Varian TrueBeam. We used the Phillips PinnacleÂ³ (version 16.2) for the VMAT planning. We did patient-specific QA by ArcCheck with SNC Patient (version 6.7.4). Additional analyses were done by the 3DVH (version 3.3.2) program with PDP Model Library (version 14). For the treatments with non-zero couch angles, the 3DVH required the couch angle to be zero for measurements. The plan delivery accuracy was evaluated by using the GPRs. We used three criteria: 3%/3mm, 2%/2mm, and 3%/0.01mm with a 10% dose threshold. We used the ArcCheck for the 2D GPR data and the ArcCheck plus 3DVH for evaluating the 3D GPR and the differences in the DVH parameters of PTVs and normal structures between the delivery and the treatment plans.
Results: The ArcCheck-3DVH system worked smoothly for the 3D GPR and DVH analyses of the complicated VMAT delivery technique used for this study. There was a weak correlation between the 2D and 3D GPRs for all three criteria. We observed a strong negative correlation between the 2D GPRs and the differences in the DVH parameters for the 3%/3mm and 2%/2mm criteria, indicating the possibility of 2D GPR as a DVH difference predictor.
Conclusion: The 92% threshold of 2D GPR with the 2%/2mm criterion can be used to identify plans with greater than 5 % errors of average DVH parameters without the 3D dose calculations for the DVH evaluation.