Characterization of a novel VenusX orthogonal dual-layer multileaf collimator

Abstract Background We investigated and characterized the performance of a novel orthogonal dual-layer multileaf collimator (αMLC) mounted on the LinaTech VenusX medical linear accelerator. Methods We evaluated leaf positioning accuracy and reproducibility using electronic portal imaging device (EPID) images of the picket fence test. The average, interleaf, and leaf-end transmissions of the upper, lower, and both αMLC layers were measured using an ionization chamber or EPID. The square and rhombus fields were used to evaluate the leaf penumbra of αMLC. To investigate the advantages of an orthogonal dual-layer MLC in field shaping, a right triangular pattern field, and a circular pattern field were formed using both layers and a single layer of the αMLC. These two evaluation pattern fields imaged were acquired by EPID and compared. Results The deviations in the positioning accuracy of the upper and lower MLC were 0.76 mm and 0.62 mm, respectively. Reproducibility was 0.29 mm and 0.26 mm correspondingly. The measured average transmissions were 1.86%, 1.82% and 0.03% for upper-, lower- and dual-layer MLC, respectively. The maximum interleaf transmission of the lower-layer MLC was 2.22% and 0.21% for the dual-layer. The maximum leaf-end transmissions were 23.90% and 0.44% correspondingly. Penumbra of the square field is 6.2 mm in X direction and 8.0 mm in Y direction. Average penumbras of the rhombus fields with side lengths of 5 cm and 10 cm were 3.6 mm and 4.9 mm, respectively. For the right triangular and circular fields, the fields shaped by the dual-layer of the αMLC were much closer to the planned field than the single-layer MLC. The dose undulation amplitude of the 50% isodose lines and the leaf stepping angle change of both layers was smaller than the single-layer MLC. Conclusions The αMLC benefits from its orthogonal dual-layer design. Leaf transmission, dose undulations at the field edge, and MLC field dependence of the leaf stepping angle of the dual-layer αMLC were remarkably reduced. αMLC can potentially improve the quality of IMRT and VMAT plans.