Characterization of an add-on multileaf collimator for electron beam therapy
Characterization of an add-on multileaf collimator for electron beam therapy
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DOI：
10.1088/0031-9155/53/4/017
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发表时间：
2008-02-21
影响因子：
3.5
通讯作者：
Schmidt, R.
中科院分区：
文献类型：
--
作者：
Gauer, T.;Sokoll, J.;Schmidt, R.
一种用于电子的附加多叶准直器（eMLC）已经被开发，其提供计算机控制的射束准直和等中心剂量递送。设计参数来自Gauer等人的设计研究（2006 Phys.Med.Biol.515987 -6003），并且被配置为使得具有机动叶片的紧凑且轻质的eMLC可以在工业上制造并稳定地安装在常规线性加速器上。在本研究中，根据能量和强度调制治疗技术的设计目标和性能，检查了初始计算机控制原型的效率。本研究集中于附件和机架稳定性以及中心轴和离轴剂量的剂量测定特性、射野大小依赖性、准直器散射、射野邻接、辐射泄漏和加速器钳口的设置。为了提供等中心照射，可通过可互换支架将eMLC放置在等中心上方16或28 cm处。该功能的机械实现导致在90度和270度机架角度下的最大场位移小于0.6 mm。与6-14 MeV的10 x 10 cm施加器相比，准直器到等中心距离为16 cm的eMLC的射束半影大0.8-0.4 cm，深度-剂量曲线显示更大的累积效应。由于治疗范围的能量依赖性损失以及小射束尺寸下的低得多的剂量输出，需要3 x 3 cm的最小射束尺寸以避免次优剂量输送。当中心轴被阻挡时，准直器散射不影响剂量输出和射束对称性。由于较宽的光束半影，在垂直和倾斜光束入射时，在相邻光束的结区测量到均匀的剂量分布。然而，具有6至14 MeV的射束能量的高差的相邻射束在邻接区域中产生大约15%的冷点和热点。为了提高均匀性，相邻束的能量必须分别限制在6至10 MeV和10至14 MeV。在14 MeV的最大可用射束能量下，辐射泄漏主要由约2.5%相对剂量的叶内泄漏引起，其可以通过将钳口射野尺寸调整到eMLC的相应开口而在远离射野边缘的离轴距离处有效地消除。另外，采用舌槽型叶片和叶片端部分别离轴连接可以减少叶间和叶端泄漏。
An add- on multileaf collimator for electrons (eMLC) has been developed that provides computer- controlled beam collimation and isocentric dose delivery. The design parameters result from the design study by Gauer et al (2006 Phys. Med. Biol. 51 5987-6003) and were configured such that a compact and lightweight eMLC with motorized leaves can be industrially manufactured and stably mounted on a conventional linear accelerator. In the present study, the efficiency of an initial computer- controlled prototype was examined according to the design goals and the performance of energy- and intensity- modulated treatment techniques. This study concentrates on the attachment and gantry stability as well as the dosimetric characteristics of central- axis and off- axis dose, field size dependence, collimator scatter, field abutment, radiation leakage and the setting of the accelerator jaws. To provide isocentric irradiation, the eMLC can be placed either 16 or 28 cm above the isocentre through interchangeable holders. The mechanical implementation of this feature results in a maximum field displacement of less than 0.6 mm at 90 degrees and 270 degrees gantry angles. Compared to a 10 x 10 cm applicator at 6-14 MeV, the beam penumbra of the eMLC at a 16 cm collimator- to- isocentre distance is 0.8-0.4 cm greater and the depth-dose curves show a larger build- up effect. Due to the loss in energy dependence of the therapeutic range and the much lower dose output at small beam sizes, a minimum beam size of 3 x 3 cm is necessary to avoid suboptimal dose delivery. Dose output and beam symmetry are not affected by collimator scatter when the central axis is blocked. As a consequence of the broader beam penumbra, uniform dose distributions were measured in the junction region of adjacent beams at perpendicular and oblique beam incidence. However, adjacent beams with a high difference in a beam energy of 6 to 14 MeV generate cold and hot spots of approximately 15% in the abutting region. In order to improve uniformity, the energy of adjacent beams must be limited to 6 to 10 MeV and 10 to 14 MeV respectively. At the maximum available beam energy of 14 MeV, radiation leakage results mainly from the intraleaf leakage of approximately 2.5% relative dose which could be effectively eliminated at off- axis distances remote from the field edge by adjusting the jaw field size to the respective opening of the eMLC. Additionally, the interleaf and leaf- end leakage could be reduced by using a tongue- and- groove leaf shape and adjoining the leaf- ends off- axis respectively.