OBJECTIVE Since most radiation treatment plans are based on computed tomography (CT) images, which makes it difficult to define the targeted tumor volume located near a metal implant, this study aims to evaluate and compare three treatment plans in order to optimally reduce geometrical uncertainty in external radiation treatment of localized prostate cancer. METHODS Experimental subjects were three prostate patients with bilateral hip prosthesis who had undergone radical radiotherapy. The treatment plans were five-field three-dimensional conformal radiation therapy (3D-CRT), fixed 5-field intensity-modulated radiation therapy (IMRT) using similar gantry angles, and single-arc volumetric modulated arc therapy (VMAT). The monitor units (MUs), dose volume histograms (DVHs), the dose indices of planning target volume (PTV), clinical target volume (CTV) and rectum were compared among the three techniques. The geometrical uncertainties were evaluated by shifting the iso-center (2- 10 mm in the anterior, posterior, left, right, superior, and inferior directions). The CTV and rectum dose indexes with and without the iso-center shifts were compared in each plan. RESULTS The Conformity Index of PTV were 1.35 in 3D-CRT, 1.12 in IMRT, and 1.04 in VMAT, respectively. The rectum doses in 3D-CRT are also higher than those in IMRT and VMAT. The iso-center shift little affected the CTV dose when smaller than the margin size. The rectum dose increased especially after a posterior shift. Additionally, this dose increase was larger in the VMAT plan than in the 3D- CRT plan. However, the VMAT achieved a superior rectum DVH to that of 3D- CRT, and this effect clearly exceeded the rectum-dose increase elicited by the iso-center shift. CONCLUSION For radiotherapy treatment of localized prostate cancer in patients with hip prosthesis, the dose distribution was better in the VMAT and Metal Artifact Reduction (MAR)-CT image methods than the conventional methods. Because the anatomical structure of the male pelvic region is relatively constant among individuals, we consider that VMAT is a valid treatment plan despite analyzing just three cases.

中文翻译：

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使用3D-CRT，IMRT和VMAT评估双侧金属髋关节假体患者局部前列腺放射治疗的几何不确定性：一项计划研究。

目的由于大多数放射治疗计划均基于计算机断层扫描（CT）图像，因此难以定义位于金属植入物附近的目标肿瘤体积，因此本研究旨在评估和比较三种治疗计划，以最佳地降低手术中的几何不确定性。外照射治疗局限性前列腺癌。方法实验对象为三例接受双侧髋关节假体治疗的前列腺癌患者。治疗计划是五场三维共形放射治疗（3D-CRT），使用相似龙门角度的固定5场强度调制放射治疗（IMRT）和单弧容积调制弧光治疗（VMAT）。监视单位（MU），剂量体积直方图（DVH），计划目标体积的剂量指数（PTV），比较了三种技术的临床目标体积（CTV）和直肠。通过移动等角点（在前，后，左，右，上和下方向2-10 mm）评估几何不确定性。在每个计划中比较了具有和不具有等中心线偏移的CTV和直肠剂量指数。结果PTV的合格指数在3D-CRT中为1.35，在IMRT中为1.12，在VMAT中为1.04。3D-CRT中的直肠剂量也高于IMRT和VMAT中的直肠剂量。当小于边缘尺寸时，等中心偏移几乎不会影响CTV剂量。直肠剂量增加，尤其是在后移之后。此外，VMAT计划中的剂量增加量大于3D-CRT计划中的剂量增加量。但是，VMAT的直肠DVH优于3D-CRT，并且这种作用明显超过了等中心点偏移引起的直肠剂量增加。结论对于髋关节假体患者的局部前列腺癌的放射治疗，VMAT和金属伪影减少（MAR）-CT图像方法的剂量分布比常规方法更好。由于男性骨盆区域的解剖结构在个体之间相对恒定，因此尽管仅分析了三例，但我们认为VMAT是一种有效的治疗方案。