Jabbari Keyvan, Rostampour Masoumeh, Roayaei Mahnaz
Assistant Professor, Clinical Medical Physicist Department of Medical Physics and Medical Engineering School of Medicine Isfahan University of Medical Sciences Isfahan, Iran..
J Appl Clin Med Phys. 2014 Jul 8;15(4):4649. doi: 10.1120/jacmp.v15i4.4649.
Titanium (Ti) mesh plates are used as a bone replacement in brain tumor surgeries. In the case of radiotherapy, these plates might interfere with the beam path. The purpose of this study is to evaluate the effect of titanium mesh on the dose distribution of electron fields. Simulations were performed using Monte Carlo BEAMnrc and DOSXYZnrc codes for 6 and 10 MeV electron beams. In Monte Carlo simulation, the shape of the titanium mesh was simulated. The simulated titanium mesh was considered as the one which is used in head and neck surgery with a thickness of 0.055 cm. First, by simulation, the percentage depth dose was obtained while the titanium mesh was present, and these values were then compared with the depth dose of homogeneous phantom with no titanium mesh. In the experimental measurements, the values of depth dose with titanium mesh and without titanium mesh in various depths were measured. The experiments were performed using a RW3 phantom with GAFCHROMIC EBT2 film. The results of experimental measurements were compared with values of depth dose obtained by simulation. In Monte Carlo simulation, as well as experimental measurements, for the voxels immediately beyond the titanium mesh, the change of the dose were evaluated. For this purpose the ratio of the dose for the case with titanium to the case without titanium was calculated as a function of titanium depth. For the voxels before the titanium mesh there was always an increase of the dose up to 13% with respect to the same voxel with no titanium mesh. This is because of the increased back scattering effect of the titanium mesh. The results also showed that for the voxel right beyond the titanium mesh, there is an increased or decreased dose to soft tissues, depending on the depth of the titanium mesh. For the regions before the depth of maximum dose, there is an increase of the dose up to 10% compared to the dose of the same depth in homogeneous phantom. Beyond the depth of maximum dose, there was a 16% decrease in dose. For both 6 and 10 MeV, before the titanium mesh, there was always an increase in dose. If titanium mesh is placed in buildup region, it causes an increase of the dose and could lead to overdose of the adjacent tissue, whereas if titanium mesh is placed beyond the buildup region, it would lead to a decrease in dose compared to the homogenous tissue.
钛（Ti）网板在脑肿瘤手术中用作骨替代物。在放射治疗的情况下，这些板可能会干扰射线路径。本研究的目的是评估钛网对电子束剂量分布的影响。使用蒙特卡罗BEAMnrc和DOSXYZnrc代码对6和10 MeV电子束进行了模拟。在蒙特卡罗模拟中，模拟了钛网的形状。模拟的钛网被视为用于头颈手术的厚度为0.055 cm的钛网。首先，通过模拟，在存在钛网的情况下获得百分深度剂量，然后将这些值与没有钛网的均匀体模的深度剂量进行比较。在实验测量中，测量了在不同深度有钛网和无钛网时的深度剂量值。实验使用带有GAFCHROMIC EBT2胶片的RW3体模进行。将实验测量结果与模拟获得的深度剂量值进行比较。在蒙特卡罗模拟以及实验测量中，对于紧邻钛网之外的体素，评估了剂量变化。为此，计算了有钛网情况与无钛网情况的剂量比作为钛深度的函数。对于钛网之前的体素，相对于没有钛网的相同体素，剂量总是增加高达13%。这是由于钛网的反向散射效应增加。结果还表明，对于紧邻钛网之外的体素，对软组织的剂量会增加或减少，这取决于钛网的深度。对于最大剂量深度之前的区域，与均匀体模中相同深度的剂量相比，剂量增加高达10%。在最大剂量深度之后，剂量降低了16%。对于6和10 MeV两者，在钛网之前，剂量总是增加。如果将钛网放置在剂量建成区，会导致剂量增加并可能导致相邻组织过量照射，而如果将钛网放置在剂量建成区之外，与均匀组织相比会导致剂量降低。
