Abstract
The resolution of multileaf collimators (MLCs) is limited by their finite leaf width. A commercial package (HD‐270™) uses 3D couch translation and leaf adjustments to emulate smaller leaf widths. In this paper, we report on the commissioning of this feature using software testing, dial gauge measurements, and film dosimetry. We also identify a variety of limitations: software bugs and truncation artifacts, MLC leaf positioning uncertainties (random variations, systematic gantry dependence and backlash), and uncertainties in couch positioning. These reduce the capabilities of this implementation below that achievable theoretically.PACS numbers: 87.53.Kn, 87.53.Uv, 87.53.Xd
Highlights
The finite leaf pitch of multileaf collimators (MLCs) limits their ability to conform to a blocked field shape.[1]. This has been identified as a major factor in the nonuse of MLCs on an MLC machine in the AAPM MLC survey.[2]. It has been proposed that conformation be improved by moving the patient perpendicular to the direction of leaf motion by less than the leaf spacing, reconforming to the shape
This has been shown to be quite effective in both theory[3] and measurement.[4]. The HD-270TM is a complete clinical system developed for conveniently delivering such a treatment on Siemens PrimusTM LINACs
Dosimetric performance We investigated the performance of the system using films of a 45° field edge generated by a stepped MLC, the angle most commonly used in the literature.[3,4,7,9] The films were taken at the isocenter of a 6-MV beam with 4 cm of solid water
Summary
The finite leaf pitch of multileaf collimators (MLCs) limits their ability to conform to a blocked field shape.[1]. This paper looks at the performance of the system and identifies some limitations in its use
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