Kuterdem H G, Cho P S
Department of Electrical Engineering, University of Washington, Seattle, Washington 98195-6043, USA.
Med Phys. 2001 Jun;28(6):894-902. doi: 10.1118/1.1373673.
The creation of arbitrary photon fluence patterns for intensity modulated radiotherapy is addressed. The proposed method is intended for a class of multileaf collimators with a requirement for minimum leaf separation. Unlike the solution of Convery and Webb in which discrete beam intensity modulation was assumed, the present method deals with continuous modulation or that consisting of infinitely small bixels. The method begins with the time-optimal solution of Spirou-Stein-Svensson disregarding the minimum gap requirement. Subsequently, the gaps are restored by mobilizing the secondary beam blocking devices to prevent overexposure resulting from the leaf separation process. The secondary beam blocking is provided by means of two orthogonal backup diaphragms that are computer controlled. The results indicate that the method can be used to accurately deliver the desired modulation while satisfying the leaf positioning constraints. Furthermore, an example is presented which illustrates the efficacy of using the horizontal backup diaphragms (moving in perpendicular direction of the leaves) in addition to the vertical backup diaphragms (moving in the parallel direction of the leaves) to generate zero fluence regions.
本文探讨了用于调强放射治疗的任意光子注量模式的创建。所提出的方法适用于一类对叶片最小间距有要求的多叶准直器。与Convery和Webb的解决方案不同，后者假设采用离散束强度调制，而本方法处理的是连续调制或由无限小的像素组成的调制。该方法首先从Spirou-Stein-Svensson的时间最优解开始，而不考虑最小间隙要求。随后，通过调动二次束阻挡装置来恢复间隙，以防止因叶片分离过程导致的过度曝光。二次束阻挡由两个计算机控制的正交备用隔板提供。结果表明，该方法可用于在满足叶片定位约束的同时准确地传递所需的调制。此外，还给出了一个示例，说明了除了垂直备用隔板（沿叶片平行方向移动）之外，使用水平备用隔板（沿叶片垂直方向移动）来生成零注量区域的效果。
