Cilla Savino, Viola Pietro, Azario Luigi, Grimaldi Luca, Craus Maurizio, D'Onofrio Guido, Fidanzio Andrea, Morganti Alessio Giuseppe, Piermattei Angelo
U.O. Fisica Sanitaria Centro di Ricerca e Formazione ad Alta Tecnologia nelle Scienze Biomediche, Università Cattolica S. Cuore, Campobasso Italy.
J Appl Clin Med Phys. 2006 Aug 24;7(3):65-79. doi: 10.1120/jacmp.v7i3.2281.
A new 2D array Seven 29T model (PTW, Freiburg), equipped with 729 vented plane-parallel ion chambers, projected for pretreatment verification of radiotherapy plans, was used as a detector for the transmitted or portal dose measurements below a Rando phantom. The dosimetric qualities of the 2D array make it attractive for measuring transmitted dose maps from step-and-shoot intensity-modulated radiotherapy (IMRT). It is well known that for step-and-shoot IMRT beams that use a small number of monitor units (MUs) per sequence, the early and recent electronic portal imaging devices (EPIDs) present a different response at X-ray start-up that affects the accuracy of the measured transmitted dose. The comparison of portal doses measured to those calculated by a commercial treatment-planning system (TPS) can verify correct dose delivery during treatment. This direct validation was tested by irradiating a simulated head tumor in a Rando anthropomorphic phantom by step-and-shoot IMRT beams. The absolute transmitted doses on a plane orthogonal to the beam central axis below the phantom were measured by the 2D array calibrated in terms of dose to water and compared with the computed portal dose extracted by custom software. In a previous paper, the comparison between the IMRT portal doses, computed by a commercial TPS and measured by a linear array that supplied a 1 mm spatial dose resolution, was carried out. The gamma-index analysis supplied an agreement of more than 95% of the dose point with acceptance criteria, in terms of dose difference, DeltaDmax, and distance agreement, deltadmax, equal to 4% and 4 mm, respectively. In this paper, we verify the possible use of the PTW 2D array for measurements of the transmitted doses during several fractions of head and neck tumor radiotherapy. There are two advantages in the use of this 2D array as a portal dose device for the IMRT quality assurance program: first is the ability to perform absolute dose comparisons for hundreds of measurement positions to verify the correct dose delivery in several fractions of the therapy; second is the efficiency in time to detect these kinds of dose distributions within the field of view area of the CT scanner.
一种新型二维阵列Seven 29T模型（PTW，弗莱堡），配备729个通风平面平行电离室，用于放疗计划的预处理验证，被用作在兰多人体模型下方测量透射剂量或射野剂量的探测器。二维阵列的剂量学特性使其在测量静态调强放疗（IMRT）的透射剂量图方面具有吸引力。众所周知，对于每个序列使用少量监测单位（MU）的静态IMRT射束，早期和近期的电子射野成像设备（EPID）在X射线启动时呈现不同的响应，这会影响所测量透射剂量的准确性。将测量的射野剂量与商业治疗计划系统（TPS）计算的剂量进行比较，可以验证治疗期间剂量的正确输送。通过用静态IMRT射束照射兰多人体模型中的模拟头部肿瘤来测试这种直接验证。通过根据水的剂量进行校准的二维阵列测量模型下方与射束中心轴正交平面上的绝对透射剂量，并与通过定制软件提取的计算射野剂量进行比较。在之前的一篇论文中，进行了由商业TPS计算的IMRT射野剂量与由提供1毫米空间剂量分辨率的线性阵列测量的剂量之间的比较。伽马指数分析表明，在剂量差异DeltaDmax和距离一致性deltadmax分别等于4%和4毫米的接受标准方面，超过95%的剂量点符合要求。在本文中，我们验证了PTW二维阵列在头颈部肿瘤放疗多个分次期间测量透射剂量的可能性。将这种二维阵列用作IMRT质量保证计划的射野剂量装置有两个优点：一是能够对数百个测量位置进行绝对剂量比较，以验证治疗多个分次中的剂量正确输送；二是在CT扫描仪视野区域内检测这类剂量分布的时间效率。
