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Medical linear accelerator x-ray sources: variation with make model and time

机译：医用线性加速器X射线源：制造模型和时间不同

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Abstract: One difficulty in radiation therapy is ensuring the correct placement of the radiation field so that the radiation is delivered to the diseased regions while healthy tissues are spared. Currently, field placement is assessed by producing a transmission radiograph (portal image) using the high-energy treatment beam. Often the quality of these images is poor. One factor which influences image quality is the size of the x-ray source found in medical linear accelerators. These sources can be large and thus reduce the spatial resolution of the portal images, thereby reducing our ability to detect bony anatomical landmarks. The high energy of the x rays generated in these accelerators make it impossible to measure the x-ray source using standard techniques (e.g., pin-hole camera or star-patterns). We have developed a reconstruction technique which allows quantitative measurement of these sources. Using this technique, we have investigated and compared the size and shape of x-ray sources on a total of seven accelerators. These include: (1) two Varian Clinac 2100cs, (2) two Atomic Energy of Canada Ltd. (AECL) Therac 6s, (3) a Varian Clinac 600c, (4) an AECL Therac 25, and (5) a Therac 20. The comparisons also include monitoring the size and shape of the sources over a two year period. For each of these measured sources the source MTF has been calculated at typical magnifications. It has been found that (1) the size and shape of the source spot varies greatly between accelerators of different design; (2) for accelerators of the same design, however, the source spots were similar; and (3) the spatial resolution of currently available on-line verification imaging systems is only marginally reduced by the size and shape these source spots. !21
机译：摘要：放射治疗的一个困难是确保正确放置放射区域，以便在保留健康组织的同时将放射线传送到患病区域。当前，通过使用高能治疗束产生透射射线照片（门户图像）来评估野外放置。这些图像的质量通常很差。影响图像质量的一个因素是医用线性加速器中X射线源的大小。这些来源可能很大，因此降低了门脉图像的空间分辨率，从而降低了我们检测骨骼解剖界标的能力。这些加速器中产生的X射线的高能量使得无法使用标准技术（例如针孔照相机或星型图）来测量X射线源。我们开发了一种重建技术，可以对这些来源进行定量测量。使用这项技术，我们研究并比较了总共七个加速器上X射线源的大小和形状。其中包括：（1）两台Varian Clinac 2100cs，（2）两台加拿大原子能公司（AECL）Therac 6s，（3）Varian Clinac 600c，（4）AECL Therac 25，以及（5）Therac 20比较还包括在两年期间监视源的大小和形状。对于这些测量源中的每一个，源MTF都是以典型放大倍数计算的。已经发现：（1）在不同设计的加速器之间，源点的大小和形状有很大的不同； （2）对于相同设计的加速器，源斑点相似； （3）当前可用的在线验证成像系统的空间分辨率仅因这些源点的大小和形状而略微降低。 ！21

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