Berbeco Ross I, Neicu Toni, Rietzel Eike, Chen George T Y, Jiang Steve B
Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Phys Med Biol. 2005 Aug 21;50(16):3669-79. doi: 10.1088/0031-9155/50/16/002. Epub 2005 Jul 28.
Respiratory gating based on external surrogates is performed in many clinics. We have developed a new technique for treatment verification using an electronic portal imaging device (EPID) in cine mode for gated 3D conformal therapy. Implanted radiopaque fiducial markers inside or near the target are required for this technique. The markers are contoured on the planning CT set, enabling us to create digitally reconstructed radiographs (DRRs) for each treatment beam. During the treatment, a sequence of EPID images can be acquired without disrupting the treatment. Implanted markers are visualized in the images and their positions in the beam's eye view are calculated off-line and compared to the reference position by matching the field apertures in corresponding EPID and DRR images. The precision of the patient set-up, the placement of the beam-gating window, as well as the residual tumour motion can be assessed for each treatment fraction. This technique has been demonstrated with a case study patient, who had three markers implanted in his liver. For this patient, the intra-fractional variation of all marker positions in the gating window had a 95% range of 4.8 mm in the SI direction (the primary axis of motion). This was about the same (5 mm) as the residual motion considered in the planning process. The inter-fractional variation of the daily mean positions of the markers, which indicates the uncertainty in the set-up procedure, was within +8.3 mm/-4.5 mm (95% range) in the SI direction for this case.
许多临床机构都在进行基于外部替代物的呼吸门控。我们开发了一种新的治疗验证技术，使用电子门静脉成像设备（EPID）的电影模式进行门控三维适形治疗。该技术需要在靶区内或附近植入不透射线的基准标记物。在计划CT图像上勾勒出标记物的轮廓，使我们能够为每个治疗射束创建数字重建射线照片（DRR）。在治疗过程中，可以采集一系列EPID图像而不中断治疗。在图像中可以看到植入的标记物，并离线计算它们在射束视场中的位置，通过匹配相应EPID和DRR图像中的射野孔径与参考位置进行比较。可以对每个治疗分次评估患者摆位的精度、射束门控窗口的放置以及残余肿瘤运动。该技术已通过一名病例患者得到验证，该患者在肝脏中植入了三个标记物。对于该患者，门控窗口内所有标记物位置的分次内变化在SI方向（主要运动轴）上的95%范围为4.8mm。这与计划过程中考虑的残余运动大致相同（5mm）。该病例中，标记物每日平均位置的分次间变化表明摆位过程中的不确定性，在SI方向上为+8.3mm/-4.5mm（95%范围）。
