Lu Weiguo
TomoTherapy Incorporated, 1240 Deming Way Madison, WI 53717, USA.
Phys Med Biol. 2008 Nov 21;53(22):6491-511. doi: 10.1088/0031-9155/53/22/017.
TomoTherapy delivery is controlled by a planned, projection-wised leaf sequence (sinogram) that is optimized during treatment planning. In this paper, we developed a software solution for real-time motion compensation that delivers helical TomoTherapy plans without modifying the hardware and workflow of the TomoTherapy delivery system. Unlike the dynamic MLC-based method, our technique only requires instantaneous tumor positions, which greatly simplifies its implementation. This technique re-uses the planned sinogram by shuffling its projections and leaf sequences. In order to compensate for longitudinal tumor motion in real-time, instead of sequential execution of the planned sinogram, the projections are executed out of order. That is, we may choose a past or future projection of the planned sinogram rather than the current projection depending on tumor motion, so that the planned radiation source position of the chosen projection is the same as the radiation source position at the current delivery time in the tumor reference frame. The transverse tumor motion is further compensated for by shifting and scaling the leaf open time of the chosen projection. We tested different planned sinograms that were optimized using various synthetic tumor/OAR configurations, as well as planned sinogram of a lung cancer patient, all with zero motion margins. Various TomoTherapy machine parameters and both regular and irregular respiratory traces were used in calculations. By applying the motion-adaptive delivery (MAD) technique, the delivered dose matched the planned dose very well in both DVH and dose profiles. As for the regular and minor irregular respiration, the dose errors were well below 3 mm and 3% criteria. No hot and cold spots were noticeable. For irregular respiration with some missing breathing cycles, this method demonstrates the capability for motion margin reduction.
螺旋断层放疗（TomoTherapy）的照射由在治疗计划期间优化的按计划的、逐投影的叶片序列（正弦图）控制。在本文中，我们开发了一种用于实时运动补偿的软件解决方案，该方案可在不改变螺旋断层放疗输送系统硬件和工作流程的情况下实现螺旋断层放疗计划。与基于动态多叶准直器（MLC）的方法不同，我们的技术仅需要肿瘤的瞬时位置，这极大地简化了其实施。该技术通过重新排列其投影和叶片序列来重新使用计划的正弦图。为了实时补偿肿瘤的纵向运动，投影不是按计划正弦图的顺序执行，而是乱序执行。也就是说，我们可以根据肿瘤运动选择计划正弦图的过去或未来投影而非当前投影，以使所选投影的计划辐射源位置与肿瘤参考坐标系中当前照射时刻的辐射源位置相同。通过对所选投影的叶片打开时间进行移位和缩放，进一步补偿肿瘤的横向运动。我们测试了使用各种合成肿瘤/危及器官（OAR）配置优化的不同计划正弦图，以及一位肺癌患者的计划正弦图，所有这些都没有设置运动边界。计算中使用了各种螺旋断层放疗机器参数以及规则和不规则的呼吸轨迹。通过应用运动自适应照射（MAD）技术，在剂量体积直方图（DVH）和剂量分布中，实际照射剂量与计划剂量匹配得非常好。对于规则和轻微不规则呼吸，剂量误差远低于3毫米和3%的标准。没有明显的热点和冷点。对于有一些呼吸周期缺失的不规则呼吸，该方法显示出有减少运动边界的能力。
