Zhao Li, Moskvin Vadim P, Cheng Chee-Wai, Das Indra J
Department of Radiation Oncology, St. Jude Children's Research Hospital, Memphis, TN, United States of America.
University Hospital Cleveland Medical Center, Cleveland, OH, United States of America.
Biomed Phys Eng Express. 2020 Nov 18;6(6). doi: 10.1088/2057-1976/abc899.
Proton beam treatment is being looked favourably now in breast treatment. Tissue expanders are often placed after mastectomy that contains metallic port for saline injection which produces dose perturbations in proton beam therapy with uncertain dosimetry. Dose perturbation for a stainless-steel injection port from a breast implant is investigated in this study. Measurements, Monte-Carlo simulation, and calculated dose distribution of plans based on kVCT and MVCT images are compared. Treatment plans are performed on kVCT and MVCT images to observe the effect of metal artifact from the breast implant. The kVCT based plan underestimates the beam range due to the overestimated water equivalent thickness of the metal ports as a result of image degradation. Compared to the measurement with metal port in the proton beam, the MVCT-based treatment planning provides more accurate dose calculation than the kVCT-based results. The dose perturbation factor calculated from MVCT planning is within 10% of the measurement results while HU corrected kVCT plan still shows dose difference as large as 100% due to the incorrect range pull back calculation caused by the misrepresentation of the volume between the plastic cap and the stainless-steel base. The dose enhancement observed at the metal and solid water interface is as large as 15%, which needs to be accounted for in the planning process if there is a clinical concern. Dose reduction as large as 16% is observed with depth from 1 cm to 4 cm underneath the thickest part of the metallic port whereas lateral dose perturbation is also seen up to 7 mm. The measurement data are supported by the Monte-Carlo simulated results with a maximum dose difference of 6%. It is concluded that if proton beam is used with metallic port, MVCT imaging data is recommended. In lieu of MVCT, DECT, CT scanner with metal artifact reduction software or in the very least, extended HU range should be used to reduce the streaking artifact as well as to produce a more accurate image of the metallic port.
质子束治疗目前在乳腺癌治疗中受到青睐。乳房切除术后常放置组织扩张器，其包含用于盐水注射的金属端口，这在质子束治疗中会产生剂量扰动，且剂量测定不确定。本研究调查了乳房植入物中不锈钢注射端口的剂量扰动。比较了测量结果、蒙特卡罗模拟以及基于千伏计算机断层扫描（kVCT）和兆伏计算机断层扫描（MVCT）图像的计划计算剂量分布。在kVCT和MVCT图像上执行治疗计划，以观察乳房植入物金属伪影的影响。基于kVCT的计划由于图像退化导致金属端口的水等效厚度被高估而低估了束流射程。与质子束中带有金属端口的测量相比，基于MVCT的治疗计划比基于kVCT的结果提供更准确的剂量计算。从MVCT计划计算出的剂量扰动因子在测量结果的10%以内，而经过HU校正的kVCT计划由于塑料帽和不锈钢底座之间体积的错误表示导致射程回拉计算错误，仍显示出高达100%的剂量差异。在金属与固体水界面观察到的剂量增强高达15%，如果存在临床担忧，在计划过程中需要考虑这一点。在金属端口最厚部分下方1厘米至4厘米深度处观察到高达16%的剂量降低，同时横向剂量扰动也可达7毫米。测量数据得到蒙特卡罗模拟结果的支持，最大剂量差异为6%。得出的结论是，如果使用带有金属端口的质子束，建议使用MVCT成像数据。如果没有MVCT，应使用双能CT（DECT）、带有金属伪影减少软件的CT扫描仪，或者至少使用扩展的HU范围来减少条纹伪影，并生成更准确的金属端口图像。
