School of Physics, Mathematics, and Computing, Faculty of Engineering and Mathematical Sciences, University of Western Australia, Crawley, WA, Australia.
GenesisCare, Wembley, WA, Australia.
Med Phys. 2021 Aug;48(8):4586-4597. doi: 10.1002/mp.15070. Epub 2021 Jul 20.
The use of three-dimensional (3D) printing to develop custom phantoms for dosimetric studies in radiotherapy is increasing. The process allows production of phantoms designed to evaluated specific geometries, patients, or patient groups with a defining feature. The ability to print bone-equivalent phantoms has, however, proved challenging. The purpose of this work was to 3D print a series of three similar spine phantoms containing no surgical implants, implants made of titanium, and implants made of carbon fiber, for future dosimetric and imaging studies. Phantoms were evaluated for (a) tissue and bone equivalence, (b) geometric accuracy compared to design, and (c) similarity to one another.
Sample blocks of PLA, HIPS, and StoneFil PLA-concrete with different infill densities were printed to evaluate tissue and bone equivalence. The samples were used to develop CT to physical (PD) and effective relative electron density (RED ) conversion curves and define the settings for printing the phantoms. CT scans of the printed phantoms were obtained to assess the geometry and densities achieved. Mean distance to agreement (MDA) and DICE coefficient (DSC) values were calculated between contours defining the different materials, obtained from design and like phantom modules. HU values were used to determine PD and RED and subsequently evaluate tissue and bone equivalence.
Sample objects showed linear relationships between HU and both PD and RED for both PLA and StoneFil. The PD and RED of the objects calculated using clinical CT conversion curves were not accurate and custom conversion curves were required. PLA printed with 90% infill density was found to have a PD of 1.11 ± 0.03 g.cm and RED of 1.04 ± 0.02 and selected for tissue- equivalent phantom elements. StoneFil printed with 100% infill density showed a PD of 1.35 ± 0.03 g.cm and RED of 1.24 ± 0.04 and was selected for bone-equivalent elements. Upon evaluation of the final phantoms, the PLA elements displayed PD in the range of 1.10 ± 0.03 g.cm -1.13 ± 0.03 g.cm and RED in the range of 1.02 ± 0.03-1.06 ± 0.03. The StoneFil elements showed PD in the range of 1.43 ± 0.04 g.cm -1.46 ± 0.04 g.cm and RED in the range of 1.31 ± 0.04-1.33 ± 0.04. The PLA phantom elements were shown to have MDA of ≤1.00 mm and DSC of ≥0.95 compared to design, and ≤0.48 mm and ≥0.91 compared like modules. The StoneFil elements displayed MDA values of ≤0.44 mm and DSC of ≥0.98 compared to design and ≤0.43 mm and ≥0.92 compared like modules.
Phantoms which were radiologically equivalent to tissue and bone were produced with a high level of similarity to design and even higher level of similarity of one another. When used in conjunction with the derived CT to PD or RED conversion curves they are suitable for evaluating the effects of spinal surgical implants of varying material of construction.
使用三维（3D）打印技术为放射治疗中的剂量学研究开发定制体模的应用越来越多。该过程允许设计和生产特定几何形状、特定患者或具有特定特征的患者群体的体模。然而，制造具有骨等效性的体模具有一定挑战性。本研究的目的是 3D 打印一系列三个类似的脊柱体模，这些体模不包含手术植入物、由钛制成的植入物和由碳纤维制成的植入物，以便进行未来的剂量学和成像研究。对体模进行了以下评估：（a）组织和骨等效性；（b）与设计相比的几何精度；（c）彼此之间的相似性。
打印了一系列不同填充密度的 PLA、HIPS 和 StoneFil PLA-混凝土样本块，以评估组织和骨等效性。使用这些样本开发 CT 至物理（PD）和有效相对电子密度（RED）转换曲线，并定义打印体模的参数。对打印的体模进行 CT 扫描，以评估获得的几何形状和密度。使用设计和类似模块的不同材料的轮廓之间的平均距离一致性（MDA）和 DICE 系数（DSC）值进行评估。HU 值用于确定 PD 和 RED，并随后评估组织和骨等效性。
样本物体显示 PLA 和 StoneFil 的 HU 值与 PD 和 RED 之间均存在线性关系。使用临床 CT 转换曲线计算的物体 PD 和 RED 不准确，需要使用定制转换曲线。发现填充密度为 90%的 PLA 打印体模的 PD 为 1.11±0.03 g.cm，RED 为 1.04±0.02，适用于组织等效体模元素。填充密度为 100%的 StoneFil 打印体模的 PD 为 1.35±0.03 g.cm，RED 为 1.24±0.04，适用于骨等效元素。在评估最终体模时，PLA 元素显示 PD 在 1.10±0.03 g.cm 至 1.13±0.03 g.cm 范围内，RED 在 1.02±0.03 至 1.06±0.03 范围内。StoneFil 元素显示 PD 在 1.43±0.04 g.cm 至 1.46±0.04 g.cm 范围内，RED 在 1.31±0.04 至 1.33±0.04 范围内。PLA 体模元素的 MDA 为≤1.00 mm，DSC 为≥0.95 与设计相比，≤0.48 mm，DSC 为≥0.91 与类似模块相比。StoneFil 元素的 MDA 值为≤0.44 mm，DSC 为≥0.98 与设计相比，≤0.43 mm，DSC 为≥0.92 与类似模块相比。
制作了具有高组织和骨等效性以及与设计高度相似性的体模，甚至与类似模块具有更高的相似性。当与衍生的 CT 至 PD 或 RED 转换曲线一起使用时，它们适用于评估不同材料构建的脊柱手术植入物的影响。
