To implement a multi-field-optimization (MFO) technique for treating patients with high-Z implants in pencil beam scanning proton-therapy and generate treatment plans that avoids small implants. Two main issues were addressed: (i) the assessment of the optimal CT acquisition and segmentation technique to define the dimension of the implant and (ii) the distance of pencil beams from the implant (avoidance margin) to assure that it does not affect dose distribution. Different CT reconstruction protocols (by O-MAR or standard reconstruction and by 12 bit or 16 bit dynamic range) followed by thresholding segmentation were tested on a phantom with lead spheres of different sizes. The proper avoidance margin was assessed on a dedicated phantoms of different materials (copper/tantalum and lead), shape (square slabs and spheres) and detectors (two-dimensional array chamber and radio-chromic films). The method was then demonstrated on a head-and-neck carcinoma patient, who underwent caro...

中文翻译：

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一种避免方法，以最大程度地减少质子笔束扫描治疗小高Z植入物患者的剂量扰动效应

在铅笔束扫描质子治疗中实施多场优化（MFO）技术来治疗高Z植入物患者，并制定避免小植入物的治疗计划。解决了两个主要问题：（i）评估最佳的CT采集和分割技术以定义植入物的尺寸；（ii）笔形束与植入物的距离（回避余量），以确保不影响剂量分配。在具有不同大小的铅球的体模上测试了不同的CT重建协议（通过O-MAR或标准重建以及12位或16位动态范围），然后进行阈值分割。根据不同材料（铜/钽和铅）的专用模型评估了适当的回避余量，形状（方形平板和球体）和检测器（二维阵列室和放射致变色膜）。然后在接受颈动脉瘤治疗的头颈癌患者中证明了该方法。