Nuclear Engineering Department, Federal University of Minas Gerais, Belo Horizonte, Brazil.
Radiat Oncol. 2013 Jul 6;8:168. doi: 10.1186/1748-717X-8-168.
Glioblastoma multiforme (GBM) is the most common, aggressive, highly malignant and infiltrative of all brain tumors with low rate of control. The main goal of this work was to evaluate the spatial dose distribution into a GBM simulator inside a head phantom exposed to a 15 MV 3D conformal radiation therapy in order to validate internal doses. A head and neck phantom developed by the Ionizing Radiation Research Group (NRI) was used on the experiments. Such phantom holds the following synthetic structures: brain and spinal cord, skull, cervical and thoracic vertebrae, jaw, hyoid bone, laryngeal cartilages, head and neck muscles and skin. Computer tomography (CT) of the simulator was taken, capturing a set of contrasted references. Therapy Radiation planning (TPS) was performed based on those CT images, satisfying a 200 cGy prescribed dose split in three irradiation fields. The TPS assumed 97% of prescribed dose cover the prescribed treatment volume (PTV). Radiochromic films in a solid water phantom provided dose response as a function of optical density. Spatial dosimetric distribution was generated by radiochromic film samples at coronal, sagittal-anterior and sagittal-posterior positions, inserted into tumor simulator and brain. The spatial dose profiles held 70 to 120% of the prescribed dose. In spite of the stratified profile, as opposed to the smooth dose profile from TPS, the tumor internal doses were within a 5% deviation from 214.4 cGy evaluated by TPS. 83.2% of the points with a gamma value of less than 1 (3%/3mm) for TPS and experimental values, respectively. At the tumor, measured at coronal section, a few dark spots in the film caused the appearance of outlier points in 13-15% of dose deviation percentage. And, as final conclusion, such dosimeter choice and the physical anthropomorphic and anthropometric phantom provided an efficient method for validating radiotherapy protocols.
多形性胶质母细胞瘤（GBM）是最常见、侵袭性最强、恶性程度最高的脑肿瘤之一，控制率低。这项工作的主要目的是评估头部体模内 GBM 模拟器在接受 15MV 3D 适形放疗时的空间剂量分布，以验证内部剂量。实验中使用了电离辐射研究组（NRI）开发的头颈部体模。这种体模具有以下合成结构：脑和脊髓、颅骨、颈椎和胸椎、下颌、舌骨、喉软骨、头颈部肌肉和皮肤。对模拟器进行了计算机断层扫描（CT），捕获了一组对比参考。基于这些 CT 图像进行了治疗放射计划（TPS），满足了 200cGy 规定剂量在三个照射野中的分割。TPS 假设 97%的规定剂量覆盖规定的治疗体积（PTV）。固体水体模中的放射色胶片提供了剂量响应与光密度的函数关系。通过将放射色胶片样本插入肿瘤模拟器和大脑中，在冠状、矢状前和矢状后位置生成空间剂量分布。空间剂量分布保持了 70%至 120%的规定剂量。尽管分层分布与 TPS 的平滑剂量分布相反，但肿瘤内部剂量在 TPS 评估的 214.4cGy 的 5%偏差范围内。TPS 和实验值的伽马值小于 1（3%/3mm）的点分别为 83.2%和 83.2%。在肿瘤处，在冠状切片上测量时，胶片上的几个暗点导致 13-15%的剂量偏差百分比出现异常点。总之，这种剂量计选择和物理人体模型和人体测量体模为验证放射治疗方案提供了一种有效的方法。
