Implementation of PTW 1600SRS detector array for multi-leaf collimator quality assurance: Picket Fence and Spoke Shot tests case study

Multi-Leaf Collimator is one of the most complex mechanical components of current medical linear accelerators which require more efficient and accurate quality assurance programs to be implemented. The main purpose of our work is to integrate a detector array to perform an objective analysis of classical MLC tests. A PTW SRS1600 array was sandwiched between upper and lower blocks of PMMA slabs. Two main mechanical tests, including picket fence and spoke shot, were designed in the treatment planning system on the acquired DICOM files of the measurement phantom. The sandwiched array is then irradiated under a VersaHD linac and the corresponding 2%/2mm and 1%/1mm GPR were acquired in the measurement week and the latter one. 2%/2mm is globally higher than 1%/1mm. For the spoke shot test, 2%/2mm decreases from the initial value at θ = 0˝ to the last angle at θ = 340˝ except for the 5mm aperture width measured the later week. For the 1%/1mm GPR criterion, all plots show a decreased value between θ = 200˝ and θ = 200˝ related to inaccurate MLC rotation. GPR-based picket fence shows a more stable variation of 2%/2mm for both 3mm and 5mm picket widths. For 3mm, a decreased value was observed at the central gap for both 2%/2mm and 1%/1mm, which disappears with a 5mm gap width. A detector array could be a beneficial approach for MLC QA, especially for objective analysis, performance reproducibility tracking, and system accuracy variation.