Dose perturbations and image artifacts caused by carbon-coated ceramic and stainless steel fiducials used in proton therapy for prostate cancer
Dose perturbations and image artifacts caused by carbon-coated ceramic and stainless steel fiducials used in proton therapy for prostate cancer
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DOI：
10.1088/0031-9155/55/23/s13
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发表时间：
2010-12-07
影响因子：
3.5
通讯作者：
Newhauser, Wayne D.
中科院分区：
文献类型：
--
作者：
Cheung, Joey;Kudchadker, Rajat J.;Newhauser, Wayne D.
使用植入的基准标记的图像引导放射治疗是用于前列腺定位以提高靶向准确性的常见解决方案。然而，通常用于常规光子放射治疗的基准点在接受质子放射治疗的患者中引起大剂量扰动。提出的解决方案是使用较低原子序数（Z）材料的基准来最小化组织中的这种效应，但是这些基准对剂量分布的影响尚未被量化。本研究的目的是分析由选定的较低Z基准点（碳涂层二氧化锆基准点和塑料涂层不锈钢基准点）引起的剂量扰动幅度，并将其与传统金基准点引起的扰动进行比较。使用体模集评估对剂量影响的选定组分。首先，在我们的质子治疗中心，使用传统的计算机断层扫描（CT）和机载千伏成像设备对基准点进行了放射学可见性评估。还在单独的体模中测量了来自基准点的CT条纹伪影。其次，使用辐射变色胶片测量基准点下游的剂量扰动。剂量扰动的大小被表征为标记材料、植入深度和相对于射束轴的方向的函数。标记的射线可见性被认为可用于临床使用。剂量测量结果表明，位于质子束调制中心附近的垂直取向的二氧化锆和不锈钢基准点对剂量的扰动小于10%，但在束范围末端附近的平行取向的相同基准点对剂量的扰动高达38%。这表明，碳涂层和不锈钢基准可以用于质子治疗，如果它们位于远离束的范围的端部，如果它们被定向为垂直于束轴。
Image-guided radiation therapy using implanted fiducial markers is a common solution for prostate localization to improve targeting accuracy. However, fiducials that are typically used for conventional photon radiotherapy cause large dose perturbations in patients who receive proton radiotherapy. A proposed solution has been to use fiducials of lower atomic number (Z) materials to minimize this effect in tissue, but the effects of these fiducials on dose distributions have not been quantified. The objective of this study was to analyze the magnitude of the dose perturbations caused by select lower-Z fiducials (a carbon-coated zirconium dioxide fiducial and a plastic-coated stainless steel fiducial) and compare them to perturbations caused by conventional gold fiducials. Sets of phantoms were used to assess select components of the effects on dose. First, the fiducials were assessed for radiographic visibility using both conventional computed tomography (CT) and an on-board kilovoltage imaging device at our proton therapy center. CT streak artifacts from the fiducials were also measured in a separate phantom. Second, dose perturbations were measured downstream of the fiducials using radiochromic film. The magnitude of dose perturbation was characterized as a function of marker material, implantation depth and orientation with respect to the beam axis. The radiographic visibility of the markers was deemed to be acceptable for clinical use. The dose measurements showed that the perpendicularly oriented zirconium dioxide and stainless steel fiducials located near the center of modulation of the proton beam perturbed the dose by less than 10%, but that the same fiducials in a parallel orientation near the end of the range of the beam could perturb the dose by as much as 38%. This suggests that carbon-coated and stainless steel fiducials could be used in proton therapy if they are located far from the end of the range of the beam and if they are oriented perpendicular to the beam axis.