Medical Physics Department, ASST Grande Ospedale Metropolitano Niguarda, Milano, Italy.
Elekta AB, Stockholm, Sweden.
Tumori. 2021 Dec;107(6):NP41-NP44. doi: 10.1177/0300891621997549. Epub 2021 Feb 25.
To outline a practical method of performing prostate cancer radiotherapy in patients with bilateral metal hip prostheses with the standard resources available in a modern general hospital. The proposed workflow is based exclusively on magnetic resonance imaging (MRI) to avoid computed tomography (CT) artifacts.
This study concerns a 73-year-old man with bilateral hip prostheses with an elevated risk prostate cancer. Magnetic resonance images with assigned electron densities were used for planning purposes, generating a synthetic CT (sCT). Imaging acquisition was performed with an optimized Dixon sequence on a 1.5T MRI scanner. The images were contoured by autosegmentation software, based on an MRI database of 20 patients. The sCT was generated assigning averaged electron densities to each contour. Two volumetric modulated arc therapy plans, a complete arc and a partial one, where the beam entrances through the prostheses were avoided for about 50° on both sides, were compared. The feasibility of matching daily cone beam CT (CBCT) with MRI reference images was also tested by visual evaluations of different radiation oncologists.
The use of magnetic resonance images improved accuracy in targets and organs at risk (OARs) contouring. The complete arc plan was chosen because of 10% lower mean and maximum doses to prostheses with the same planning target volume coverage and OAR sparing. The image quality of the match between performed CBCTs and MRI was considered acceptable. The proposed method seems promising to improve radiotherapy treatments for this complex category of patients.
概述在现代综合医院标准资源条件下，为双侧金属髋关节假体患者进行前列腺癌放射治疗的实用方法。所提出的工作流程完全基于磁共振成像（MRI），以避免计算机断层扫描（CT）伪影。
本研究涉及一位 73 岁男性，双侧髋关节假体，前列腺癌风险升高。计划目的使用分配电子密度的磁共振成像，生成合成 CT（sCT）。在 1.5T MRI 扫描仪上使用优化的 Dixon 序列进行成像采集。使用自动分割软件对图像进行轮廓处理，基于 20 例患者的 MRI 数据库。sCT 通过为每个轮廓分配平均电子密度生成。比较了两种容积调强弧形治疗计划，一种是完整弧形，另一种是部分弧形，在两侧大约 50°处避开了通过假体的射束入口。还通过不同放射肿瘤学家的视觉评估测试了每日锥形束 CT（CBCT）与 MRI 参考图像匹配的可行性。
磁共振图像的使用提高了靶区和危及器官（OARs）轮廓的准确性。选择完整弧形计划是因为对于相同的计划靶区覆盖和 OAR 保护，假体的平均和最大剂量降低了 10%。进行的 CBCT 与 MRI 之间的匹配图像质量被认为是可以接受的。该方法似乎有望改善此类复杂患者的放射治疗。
