A finger leaf design for dual layer MLCs

摘要

Purpose: In current MLC designs, the shapes of leaf end (projected to the isocenter plane) are line sections. The radiation field shaped by MLC has a stepwise boundary, and is not identical to the desired target field with a smooth boundary. The purpose of this study is to introduce a finger leaf design applied to dual layer MLCs, and to evaluate the performance of the new design. Methods and Material: An optimization model was first constructed to describe the problem of determining leaf end shapes, and the corresponding problems were then solved by the adaptive simulated annealing technique. Optimal parameters for arc shapes of leaf end projections were obtained, and a comparison was done between optimized MLCs and conventional MLCs in terms of field conformity. The optimization process was based on 634 target fields selected from the patient data base of a treatment planning system. Areas of these fields ranged from 20.0 to 602.7cm2 with a mean and its standard deviation of 125.7±70.0cm2. Results: With the finger leaf design, the radiation field shaped by MLC has a smoother boundary rather than a stepwise boundary and the conformity of MLC shaped fields to the desired target fields is improved by 32.3%.