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首页> 外文会议>Conference on physics of medical imaging >X-ray Scatter in Quantitative Megavoltage Computed Tomography: Implications for Adaptive Radiation Therapy
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X-ray Scatter in Quantitative Megavoltage Computed Tomography: Implications for Adaptive Radiation Therapy

机译：定量兆伏计算机断层扫描中的X射线散射：对适应性放射治疗的影响

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The emergence of helical tomotherapy has provided a unique opportunity to combine aspects of diagnostic computed tomography and radiation treatment. Daily megavoltage computed tomography (MVCT) scans of a patient in the treatment position provide an ideal input for adaptive radiation therapy, whereby the quantitative CT knowledge of a patient from a treatment fraction combined with the knowledge of the therapy dose distribution can be used to alter and correct for the dose delivery in subsequent fractions. In order for adaptive radiotherapy to be successful, the quantitative information from the CT scan must be as accurate as possible in geometric and dosimetric information. One potential impediment to the accuracy of the CT data values is x-ray scatter. In our study, we quantify the magnitude of x-ray scatter in the tomotherapy (fan-beam) MVCT system, based on Monte Carlo simulations of the scatter-to-primary ratio (SPR) as a function of incident x-ray energy, fan-beam slice thickness, patient size, and air gap distance. Furthermore, based on these SPR values, the impact on CT number accuracy is shown, and the implications for adaptive radiotherapy (i.e. dose reconstruction) are discussed. Under conditions common to tomotherapy MVCT scanning, SPR values range from 0.02 to 0.16 (depending on the size of the phantom), and are generally lower than those encountered in diagnostic cone-beam CT and megavoltage portal imaging. These SPR values are sufficient enough to introduce CT number errors as high as 5 HU in soft-tissue and 100 HU in bone. The implication of this inaccuracy for adaptive radiotherapy would be to cause potential dose calculation errors during dose reconstruction and treatment re-planning.
机译：螺旋断层扫描的出现提供了将诊断计算机断层扫描和放射治疗相结合的独特机会。每天在治疗位置进行患者的兆伏计算机断层扫描（MVCT）扫描，为适应性放射治疗提供了理想的输入，从而可以利用来自治疗部位的患者定量CT知识与治疗剂量分布的知识相结合并校正后续阶段的剂量输送。为了使适应性放射治疗成功，来自CT扫描的定量信息在几何和剂量学信息上必须尽可能准确。 CT数据值准确性的一个潜在障碍是X射线散射。在我们的研究中，我们基于散射与主要比例（SPR）随入射x射线能量的函数的蒙特卡罗模拟，对tomotherapy（扇形光束）MVCT系统中的x射线散射量进行了量化，扇形光束切片的厚度，患者的体型和气隙距离。此外，基于这些SPR值，显示了对CT编号准确性的影响，并讨论了对适应性放射治疗（即剂量重建）的意义。在断层扫描MVCT扫描的常见条件下，SPR值在0.02到0.16（取决于体模的大小）范围内，并且通常低于诊断性锥束CT和兆电压门控成像中遇到的值。这些SPR值足以在软组织中引入高达5 HU的CT编号误差，在骨骼中引入高达100 HU的CT编号误差。这种对适应性放疗的不准确性将导致在剂量重建和治疗重新规划过程中引起潜在的剂量计算错误。

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