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.

质子束治疗现在在乳房治疗中受到青睐。组织扩张器通常在乳房切除术后放置，其中包含用于盐水注射的金属端口，这会在不确定剂量的质子束治疗中产生剂量扰动。本研究调查了来自乳房植入物的不锈钢注射口的剂量扰动。比较了基于 kVCT 和 MVCT 图像的测量、蒙特卡罗模拟和计划的计算剂量分布。对 kVCT 和 MVCT 图像执行治疗计划，以观察乳房植入物的金属伪影效果。由于图像退化导致高估金属端口的水当量厚度，基于 kVCT 的计划低估了波束范围。与质子束中金属端口的测量相比，基于 MVCT 的治疗计划提供比基于 kVCT 的结果更准确的剂量计算。MVCT 规划计算的剂量扰动因子在测量结果的 10% 以内，而 HU 校正的 kVCT 规划仍然显示剂量差异高达 100%，这是由于塑料盖和不锈钢底座。在金属和固体水界面观察到的剂量增加高达 15%，如果存在临床问题，则需要在规划过程中加以考虑。在金属端口最厚部分下方 1 cm 至 4 cm 的深度处观察到剂量减少高达 16%，而横向剂量扰动也观察到高达 7 mm。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%。结论是如果质子束与金属端口一起使用，建议使用MVCT成像数据。代替 MVCT、DECT、带有金属伪影减少软件的 CT 扫描仪或至少应使用扩展的 HU 范围来减少条纹伪影并生成更准确的金属端口图像。