Medical Physics Department, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa.
Medical Physics Department, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa.
Phys Med. 2018 Oct;54:94-102. doi: 10.1016/j.ejmp.2018.09.124. Epub 2018 Oct 3.
In radiotherapy, accurate calculation of patient radiation dose is very important for good clinical outcome. In the presence of metallic implants, the dose calculation accuracy could be compromised by metal artefacts generated in computed tomography (CT) images of patients. This study investigates the influence of metal-induced CT artefacts on MC dose calculations in a pelvic prosthesis phantom.
A pelvic phantom containing unilateral Ti prosthesis was CT-scanned and accurate Hounsfield unit (HU) values were assigned to known materials of the phantom as opposed to HU values produced through the artefact CT images of the phantom. Using the DOSXYZnrc MC code, dose calculations were computed in the phantom model constructed from the original CT images containing the artefacts and artefact-free images made from the exact geometry of the phantom with known materials. The dose calculations were benchmarked against Gafchromic EBT3 film measurements using 15 MeV electron and 10 MV photon beams.
The average deviations between film and MC dose data decreased from 3 ± 2% to 1 ± 1% and from about 6 ± 2% to 3 ± 1% for the artefact and artefact-free phantom models against film data for the electron and photon fields, respectively.
For the Ti prosthesis phantom, the presence of metal-induced CT artefacts could cause dose inaccuracies of about 3%. Construction of an artefact-free phantom model made from the exact geometry of the phantom with known materials to overcome the effect of artefacts is advantageous compared to using CT data directly of which the exact tissue composition is not well-known.
在放射治疗中，准确计算患者的辐射剂量对于获得良好的临床结果非常重要。在存在金属植入物的情况下，患者 CT 图像中产生的金属伪影会影响剂量计算的准确性。本研究旨在探讨金属诱导的 CT 伪影对骨盆假体模型中的 MC 剂量计算的影响。
对包含单侧钛假体的骨盆模型进行 CT 扫描，并为已知材料的假体分配准确的亨氏单位（HU）值，而不是通过假体 CT 图像生成 HU 值。使用 DOSXYZnrc MC 代码，在包含伪影的原始 CT 图像和由假体的精确几何形状与已知材料构建的无伪影图像构建的模型中进行剂量计算。使用 15 MeV 电子和 10 MV 光子束，通过 Gafchromic EBT3 胶片测量对剂量计算进行基准测试。
对于电子和光子场，与胶片数据相比，胶片和 MC 剂量数据之间的平均偏差分别从 3%±2%降低到 1%±1%，从约 6%±2%降低到 3%±1%，对于有伪影和无伪影的模型。
对于钛假体模型，金属诱导的 CT 伪影可能导致约 3%的剂量不准确。与直接使用 CT 数据相比，构建具有已知材料的假体精确几何形状的无伪影模型以克服伪影的影响是有利的，因为 CT 数据中并不清楚确切的组织组成。
