Perrin R L, Zakova M, Peroni M, Bernatowicz K, Bikis C, Knopf A K, Safai S, Fernandez-Carmona P, Tscharner N, Weber D C, Parkel T C, Lomax A J
Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland.
Phys Med Biol. 2017 Mar 21;62(6):2486-2504. doi: 10.1088/1361-6560/62/6/2486. Epub 2017 Feb 27.
Motion-induced range changes and incorrectly placed dose spots strongly affect the quality of pencil-beam-scanned (PBS) proton therapy, especially in thoracic tumour sites, where density changes are large. Thus motion-mitigation techniques are necessary, which must be validated in a realistic patient-like geometry. We report on the development and characterisation of a dynamic, anthropomorphic, thorax phantom that can realistically mimic thoracic motions and anatomical features for verifications of proton and photon 4D treatments. The presented phantom is of an average thorax size, and consists of inflatable, deformable lungs surrounded by a skeleton and skin. A mobile 'tumour' is embedded in the lungs in which dosimetry devices (such as radiochromic films) can be inserted. Motion of the tumour and deformation of the thorax is controlled via a custom made pump system driving air into and out of the lungs. Comprehensive commissioning tests have been performed to evaluate the mechanical performance of the phantom, its visibility on CT and MR imaging and its feasibility for dosimetric validation of 4D proton treatments. The phantom performed well on both regular and irregular pre-programmed breathing curves, reaching peak-to-peak amplitudes in the tumour of <20 mm. Some hysteresis in the inflation versus deflation phases was seen. All materials were clearly visualised in CT scans, and all, except the bone and lung components, were MRI visible. Radiochromic film measurements in the phantom showed that imaging for repositioning was required (as for a patient treatment). Dosimetry was feasible with Gamma Index agreements (4%/4 mm) between film dose and planned dose >90% in the central planes of the target. The results of this study demonstrate that this anthropomorphic thorax phantom is suitable for imaging and dosimetric studies in a thoracic geometry closely-matched to lung cancer patients under realistic motion conditions.
运动引起的范围变化和剂量点放置不当会严重影响笔形束扫描（PBS）质子治疗的质量，尤其是在胸部肿瘤部位，那里的密度变化很大。因此，运动缓解技术是必要的，并且必须在逼真的患者样几何模型中进行验证。我们报告了一种动态、拟人化胸部体模的开发和特性，该体模可以逼真地模拟胸部运动和解剖特征，用于质子和光子4D治疗的验证。所展示的体模尺寸为平均胸部大小，由充气、可变形的肺组成，周围是骨骼和皮肤。一个可移动的“肿瘤”嵌入肺中，剂量测定装置（如放射变色胶片）可以插入其中。肿瘤的运动和胸部的变形通过定制的泵系统控制，该系统将空气泵入和泵出肺部。已经进行了全面的调试测试，以评估体模的机械性能、其在CT和MR成像上的可见性以及其用于4D质子治疗剂量验证的可行性。该体模在规则和不规则的预编程呼吸曲线上表现良好，肿瘤的峰峰值幅度小于20毫米。在充气和放气阶段观察到一些滞后现象。所有材料在CT扫描中都能清晰显示，除了骨骼和肺部组件外，所有材料在MRI上都可见。体模中的放射变色胶片测量表明，需要进行成像以重新定位（如同患者治疗一样）。在靶区中心平面，胶片剂量与计划剂量之间的伽马指数一致性（4%/4毫米）>90%，剂量测定是可行的。本研究结果表明，这种拟人化胸部体模适用于在与肺癌患者密切匹配的胸部几何模型中，在实际运动条件下进行成像和剂量研究。
