Application of detector array in treatment planning system modeling adjustment

Abstract

Objective To investigate the feasibility of detector array in Monaco modeling for MLC parameters adjustment. Methods One parameter was fixed, and then the other parameter was changed. The γ pass rates of the test beams, namely 3ABUT, 7SegA, and FOUR L, were assessed to determine the values of leaf transmission and leaf offset. A total of 12 tumor cases from different anatomical sites were randomly selected. Two-dimensional dose verification (rack angle zero) of Step& Shot and dMLC plans as well as three-dimensional dose validation of VMAT plan were performed using Octavius 4D system. The γ pass rates were analyzed at a standard of 3%/3 mm. Meanwhile, the point dose verification for these three plans was analyzed to obtain the dose deviations. Results The values of leaf transmission and leaf offset were 0.0105 and-0.08 mm, respectively. The average γ pass rates (%) of Step& Shot, dMLC, and VMAT plans were 88.59±2.94, 87.81±3.28, and 87.45±2.24 before adjustment and 98.45±1.23, 98.9±1.01, and 96.03±1.66 after adjustment. In addition, the average dose deviations (%) according to the point dose verification were 0.85±0.75, 0.95±0.39, and 0.98±0.40 before adjustment and 0.97±0.57, 1.08±0.76, and 0.86±0.45 after adjustment. Conclusions Octavius detector 729 ionization chamber array is a feasible and reliable device in Monaco modeling for MLC parameters adjustment. Key words: Post modeling adjustment; Detector array; γpass rates; Leaf transmission; Leaf offset