Kemp J, Price M
Louisiana State University, Baton Rouge, LA.
Mary Bird Perkins Cancer Center, Baton Rouge, LA.
Med Phys. 2012 Jun;39(6Part14):3777. doi: 10.1118/1.4735405.
Nucletron's Oncentra Brachy Applicator Modeling plugin (AMp) may facilitate HDR cervical brachytherapy treatment planning when image artifact inhibits dwell position localization. The AMp utilizes a 3D CAD rendering of the corresponding applicator to define possible source dwell positions. This study compares the equivalence of source localization within a CT/MR Fletcher-type tandem and ovoid applicator utilizing clinical practice and Oncentra's AMp in a water phantom containing OAR surrogate structures.
KVCT image sets were acquired of a water phantom containing bladder and rectum surrogates as well as an assembled Nucletron Fletcher CT/MR applicator with various ovoid sizes (20, 25, 30mm) and a 30° tandem. Using Oncentra's Brachy TPS, OAR-surrogates were segmented and catheters were reconstructed using (1) clinical protocols (i.e. using source dwell position markers) and (2) using the AMp. Treatment plans were generated following clinical protocol, ensuring 600cGy to the ICRU 38-defined Point A. The center coordinates of each active dwell position were spatially compared. The dosimetric impact of these differences was quantified by determining D0. 1cc, D1cc and D2cc for the surrogate OARs.
Preliminary results obtained for the 25mm ovoid / 30° tandem applicator show 80% of dwell positions defined by clinical protocol and the AMp agree within 1mm with a maximum deviation of 1.17mm. Differences in source positions resulted in an increase of 2.9%, 0.48% and 0.3% and 0.66%, 0.87%, and 0.59% for D0.1cc, D1cc and D2cc for the bladder- and rectum-surrogates, respectively, when utilizing the AMp rather than clinical protocol for source position localization.
Preliminary results indicate that source dwell position localization utilizing Nucletron's Applicator Modeling plugin and our clinical protocol results in equivalent dosimetry for the simple, water phantom geometry investigated. Currently we are investigating the validity of this conclusion utilizing ovoids of different sizes as well as a CT/MR-compatible vaginal cylinder.
当图像伪影阻碍驻留位置定位时，Nucletron的Oncentra近距离放射治疗施源器建模插件（AMp）可能有助于高剂量率宫颈近距离放射治疗的治疗计划制定。AMp利用相应施源器的3D计算机辅助设计渲染来定义可能的源驻留位置。本研究比较了在含有危及器官替代结构的水模体中，利用临床实践和Oncentra的AMp在CT/MR Fletcher型串联卵圆体施源器内进行源定位的等效性。
获取含有膀胱和直肠替代物的水模体以及带有各种卵圆体尺寸（20、25、30mm）和30°串联的组装好的Nucletron Fletcher CT/MR施源器的千伏CT图像集。使用Oncentra的近距离放射治疗治疗计划系统，对危及器官替代物进行分割，并使用（1）临床方案（即使用源驻留位置标记）和（2）使用AMp重建导管。按照临床方案生成治疗计划，确保给予国际辐射单位与测量委员会（ICRU）38定义的A点600cGy。对每个活跃驻留位置的中心坐标进行空间比较。通过确定替代危及器官的D0.1cc、D1cc和D2cc来量化这些差异的剂量学影响。
对于25mm卵圆体/30°串联施源器获得的初步结果显示，临床方案和AMp定义的驻留位置中有80%在1mm范围内一致，最大偏差为1.17mm。当利用AMp而非临床方案进行源位置定位时，源位置的差异分别导致膀胱替代物和直肠替代物的D0.1cc、D1cc和D2cc增加2.9%、0.48%和0.3%以及0.66%、0.87%和0.59%。
初步结果表明，利用Nucletron的施源器建模插件和我们的临床方案进行源驻留位置定位，对于所研究的简单水模体几何结构会产生等效的剂量学结果。目前我们正在利用不同尺寸的卵圆体以及与CT/MR兼容的阴道圆柱体研究这一结论的有效性。
