Brezovich Ivan A, Popple Richard A, Duan Jun
Department of Radiation Oncology, The University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
J Appl Clin Med Phys. 2006 Aug 24;7(3):35-42. doi: 10.1120/jacmp.v7i3.2186.
A method is proposed for generating dynamic wedges spanning the entire field width, defined as the collimator opening in the wedged direction, without changes to existing hardware. The technique approximates the fluence pattern of a dynamic wedge by sequentially closing the leaves of a 120-leaf multileaf collimator (MLC). Closure times for the individual leaves were derived by extending the segmented treatment table of the dynamic wedge provided by the manufacturer of the linear accelerator. Using film dosimetry, beam properties of MLC wedges were compared to those of conventional dynamic and mechanical wedges. Profiles and isodose lines of the MLC wedge were almost identical to those of the dynamic wedge, and differed only modestly from the mechanical counterparts. Dose inhomogeneity due to the individually closing leaves was not significant. The high-dose region at the junction between opposing MLC leaves, unavoidable when the field length (i.e., the opening of the collimator in the nonwedged direction) exceeds the maximum leaf extension of 15 cm, was feathered by moving leaf pairs after their closure for the remainder of the irradiation time. Combining the MLC wedge with a regular dynamic wedge to reduce the line of high dose under the leaf junction is under consideration.
本文提出了一种在不改变现有硬件的情况下生成跨越整个射野宽度（定义为楔形方向上的准直器开口）的动态楔形板的方法。该技术通过依次关闭120叶多叶准直器（MLC）的叶片来近似动态楔形板的注量分布。单个叶片的关闭时间是通过扩展直线加速器制造商提供的动态楔形板的分段治疗表得出的。使用胶片剂量学，将MLC楔形板的射束特性与传统动态楔形板和物理楔形板的特性进行了比较。MLC楔形板的剂量分布曲线和等剂量线与动态楔形板几乎相同，与物理楔形板的差异也仅为中等程度。由于叶片逐个关闭导致的剂量不均匀性并不显著。当射野长度（即非楔形方向上的准直器开口）超过最大叶片伸展长度15 cm时，在相对的MLC叶片交界处不可避免地会出现高剂量区域，通过在剩余照射时间内叶片对关闭后移动叶片对来使其变平滑。正在考虑将MLC楔形板与常规动态楔形板结合使用，以减少叶片交界处下方的高剂量线。
