Meltsner Sheridan, Craciunescu Oana, Raffi Julie, Lee Casey, Sheng Yang, Chino Junzo, Ayala-Peacock Diandra, Kim Yongbok
Department of Radiation Oncology, Duke University, Durham, North Carolina, USA.
J Appl Clin Med Phys. 2025 Feb;26(2):e14605. doi: 10.1002/acm2.14605. Epub 2024 Dec 17.
This paper outlines the commissioning of the Varian (VMS, Varian Medical Systems, Palo Alto, CA) Universal Interstitial Cylinder (UIC) applicator set for Ir-192 HDR brachytherapy. The UIC was commissioned for use with CT and MRI and a custom phantom was designed to avoid the introduction of water-like materials into the needle guide tracks. Various marker strands were investigated to determine which allowed the most accurate reconstruction of source positions.
Planar kV and MV imaging, along with physical measurements and autoradiographs, were used to commission the physical dimensions of all components of the UIC applicator set. CT and MR imaging was used to further commission one configuration of the UIC with UCP and eight interstitial needles in a simulated clinical setup using a GYN phantom. Three different methods of channel identification were compared - no radio opaque markers, VMS numbered markers, or nylon coated stainless steel leader wires - to see which best aided in channel identification and image registration. An HDR MRI Lumen marker (C4 Imaging, LLC) was used to verify any applicator rotation on MR scans during image registration. Three types of GYN phantoms were investigated - wet towel, gelatin, and ground beef. Dimensions of all components were compared with vendor provided information, including the solid applicator models, which are based on the computer-aided design model files of the specific applicators.
The dimensions of the applicators could be validated using physical measurements, kV and MV planar imaging, and CT scans. The ground beef based GYN phantom best eliminated the introduction of water into the needle guide tracks that was found when using a water or gel-based phantom. CT scans using no radio opaque markers did not allow the plastic needles to be visualized well enough to digitize source positions. CT scans with VMS markers showed significant artifact. CT scans with the nylon coated stainless steel wires provided the best visibility of the needle locations to aid in digitizing source positions. The use of an MR marker allowed the channel to be identified on the MR scan and confirm rotation for image registration.
The UIC set and applicator configuration was commissioned for CT and MR based treatment planning. The plastic components of the UIC applicator set pose challenges to the commissioning process but the use of radio opaque markers seen on CT combined with MR image registration allow the source positions within the needles, as well as the location of the end of the needles, to be digitized appropriately. A ground beef phantom minimized the fluid introduced into the needle guide track, minimizing any unintended MR and CT signal in the needle guide tracks.
本文概述了用于铱 - 192高剂量率近距离放射治疗的瓦里安（VMS，瓦里安医疗系统公司，加利福尼亚州帕洛阿尔托）通用组织间圆柱体（UIC）施源器装置的调试过程。该UIC施源器装置经调试可与CT和MRI配合使用，并且设计了一个定制体模以避免将类似水的材料引入针导轨道。研究了各种标记线，以确定哪种标记线能最准确地重建源位置。
使用平面千伏和兆伏成像，以及物理测量和放射自显影片，对UIC施源器装置的所有组件的物理尺寸进行调试。在使用妇科体模的模拟临床设置中，使用CT和MR成像对带有通用校准点（UCP）和八根组织间针的一种UIC配置进行进一步调试。比较了三种不同的通道识别方法——无放射性不透明标记、VMS编号标记或尼龙涂层不锈钢引导线——以确定哪种方法最有助于通道识别和图像配准。在图像配准期间，使用高剂量率MRI管腔标记（C4成像有限责任公司）来验证MR扫描上施源器的任何旋转。研究了三种类型的妇科体模——湿毛巾、明胶和碎牛肉。将所有组件的尺寸与供应商提供的信息进行比较，包括基于特定施源器的计算机辅助设计模型文件的实心施源器模型。
可以使用物理测量、千伏和兆伏平面成像以及CT扫描来验证施源器的尺寸。基于碎牛肉的妇科体模能最好地消除在使用水基或凝胶基体模时发现的水进入针导轨道的情况。不使用放射性不透明标记的CT扫描无法使塑料针清晰成像以数字化源位置。带有VMS标记的CT扫描显示出明显的伪影。带有尼龙涂层不锈钢丝的CT扫描能提供针位置的最佳可视性，有助于数字化源位置。使用MR标记可在MR扫描上识别通道并确认用于图像配准的旋转。
UIC装置和施源器配置已针对基于CT和MR的治疗计划进行了调试。UIC施源器装置的塑料组件给调试过程带来了挑战，但在CT上看到的放射性不透明标记与MR图像配准相结合，可使针内的源位置以及针末端的位置得到适当数字化。碎牛肉体模可将引入针导轨道的液体减至最少，从而将针导轨道中任何意外的MR和CT信号减至最少。
