Mahuvava Courage, Du Plessis Frederik Carl Phillipus
Department of Medical Physics, Faculty of Health Sciences, University of the Free State, Bloemfontein, South Africa.
J Med Phys. 2018 Oct-Dec;43(4):236-246. doi: 10.4103/jmp.JMP_70_18.
Hip prostheses (HPs) are routinely used in hip augmentation to replace painful or dysfunctional hip joints. However, high-density and high-atomic-number (Z) inserts may cause dose perturbations in the target volume and interface regions.
To evaluate the dosimetric influence of various HPs during megavoltage conformal radiotherapy (RT) of the prostate using Monte Carlo (MC) simulations.
BEAMnrc and DOSXYZnrc MC user-codes were respectively used to simulate the linac head and to calculate 3D absorbed dose distributions in a computed tomography (CT)-based phantom. A novel technique was used to synthetically introduce HPs into the raw patient CT dataset. The prosthesis materials evaluated were stainless steel (SS316L), titanium (Ti6Al4V), and ultra-high-molecular-weight polyethylene (UHMWPE). Four, five, and six conformal photon fields of 6-20 MV were used.
The absorbed dose within and beyond metallic prostheses dropped significantly due to beam attenuation. For bilateral HPs, the target dose reduction ranged up to 23% and 17% for SS316L and Ti6Al4V, respectively. For unilateral HP, the respective dose reductions were 19% and 12%. Dose enhancement was always <1% for UHMWPE. The 6-field plan produced the best target coverage. Up to 38% dose increase was found at the bone-SS316L proximal interface.
The novel technique used enabled the complete exclusion of metal artifacts in the CT dataset. High-energy plans with more oblique beams can help minimize dose attenuation through HPs. Shadowing and interface effects are density dependent and greatest for SS316L, while UHMWPE poses negligible dose perturbation.
髋关节假体（HPs）常用于髋关节增强手术，以替换疼痛或功能失调的髋关节。然而，高密度和高原子序数（Z）的植入物可能会在靶区和界面区域引起剂量扰动。
使用蒙特卡罗（MC）模拟评估前列腺兆伏级适形放疗（RT）期间各种髋关节假体的剂量学影响。
分别使用BEAMnrc和DOSXYZnrc MC用户代码模拟直线加速器机头，并在基于计算机断层扫描（CT）的体模中计算三维吸收剂量分布。采用一种新技术将髋关节假体综合引入原始患者CT数据集中。评估的假体材料为不锈钢（SS316L）、钛（Ti6Al4V）和超高分子量聚乙烯（UHMWPE）。使用了4个、5个和6个6 - 20 MV的适形光子野。
由于束流衰减，金属假体内外的吸收剂量显著下降。对于双侧髋关节假体，SS316L和Ti6Al4V的靶区剂量分别降低了23%和17%。对于单侧髋关节假体，相应的剂量降低分别为19%和12%。超高分子量聚乙烯的剂量增强始终<1%。6野计划产生了最佳的靶区覆盖。在骨 - SS316L近端界面处发现剂量增加高达38%。
所采用的新技术能够完全排除CT数据集中的金属伪影。具有更多斜束的高能计划有助于将通过髋关节假体的剂量衰减降至最低。阴影和界面效应与密度有关，对SS316L最大，而超高分子量聚乙烯引起的剂量扰动可忽略不计。
