Feasibility of a simple method of hybrid collimation for megavoltage grid therapy
Feasibility of a simple method of hybrid collimation for megavoltage grid therapy
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DOI：
10.1118/1.4801902
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发表时间：
2013-05-01
期刊：
影响因子：
3.8
通讯作者：
Roberto, Daniel
中科院分区：
文献类型：
--
作者：
Almendral, Pedro;Mancha, Pedro J.;Roberto, Daniel
目的：兆伏电网治疗目前提供的步进和射击多段技术或使用高衰减块与发散孔。然而，网格块的商业可用性是有限的，它们的构造是困难的，并且步进和发射技术需要更长的治疗时间，并且对于一些多叶准直器是不实用的。这项工作研究了一个混合准直系统的可行性，网格治疗，不需要多个部分，可以很容易地实现广泛可用的技术means.Methods：作者已经开发出一个系统，以产生一个网格的细光束，同时使用两个垂直的等距叶片，项目条纹图案在正交方向。其中一个是由集成在加速器中的多叶准直器产生的，另一个是由放射肿瘤科常用的低熔点合金制成的内部准直器产生的。6和18 MV的网格字段的特性进行了研究与屏蔽二极管，非屏蔽二极管，和radiochromic film.Results：与混合准直得到的网格是类似的一些临床上使用的网格的细光束的大小（约1厘米）和开放的光束（1/4的总字段）的百分比。网格场的穿透力不如同等能量的开放场。根据剖面的深度和方向（对角线或沿着主轴），测得的谷峰剂量比范围为5%至16%（6 MV）和9%至20%（18 MV）。所有的探测器产生类似的结果，在测量的轮廓和百分比的深度剂量，但屏蔽二极管似乎高估的输出factors.Conclusions：在正交方向的两个条纹图案准直器的组合是一种可行的方法来获得二维阵列的细光束，并具有潜在的有用性作为一种有效的方式来提供网格治疗。该方法的实现在技术上比传统网格块的构造简单。(c)2013年美国医学物理学家协会。
Purpose: Megavoltage grid therapy is currently delivered with step-and-shoot multisegment techniques or using a high attenuation block with divergent holes. However, the commercial availability of grid blocks is limited, their construction is difficult, and step-and-shoot techniques require longer treatment times and are not practical with some multileaf collimators. This work studies the feasibility of a hybrid collimation system for grid therapy that does not require multiple segments and can be easily implemented with widely available technical means.Methods: The authors have developed a system to generate a grid of beamlets by the simultaneous use of two perpendicular sets of equally spaced leaves that project stripe patterns in orthogonal directions. One of them is generated with the multileaf collimator integrated in the accelerator and the other with an in-house made collimator constructed with a low melting point alloy commonly available at radiation oncology departments. The characteristics of the grid fields for 6 and 18 MV have been studied with a shielded diode, an unshielded diode, and radiochromic film.Results: The grid obtained with the hybrid collimation is similar to some of the grids used clinically with respect to the beamlet size (about 1 cm) and the percentage of open beam (1/4 of the total field). The grid fields are less penetrating than the open fields of the same energy. Depending on the depth and the direction of the profiles (diagonal or along the principal axes), the measured valley-to-peak dose ratios range from 5% to 16% for 6 MV and from 9% to 20% for 18 MV. All the detectors yield similar results in the measurement of profiles and percent depth dose, but the shielded diode seems to overestimate the output factors.Conclusions: The combination of two stripe pattern collimators in orthogonal directions is a feasible method to obtain two-dimensional arrays of beamlets and has potential usefulness as an efficient way to deliver grid therapy. The implementation of this method is technically simpler than the construction of a conventional grid block. (c) 2013 American Association of Physicists in Medicine.