Graves Edward E, Zhou Hu, Chatterjee Raja, Keall Paul J, Gambhir Sanjiv Sam, Contag Christopher H, Boyer Arthur L
Department of Radiology Oncology, Molecular Imaging Program at Stanford, Stanford University, Stanford, California 94305, USA.
Med Phys. 2007 Nov;34(11):4359-67. doi: 10.1118/1.2789498.
Treatment of small animals with radiation has in general been limited to planar fields shaped with lead blocks, complicating spatial localization of dose and treatment of deep-seated targets. In order to advance laboratory radiotherapy toward what is accomplished in the clinic, we have constructed a variable aperture collimator for use in shaping the beam of microCT scanner. This unit can image small animal subjects at high resolution, and is capable of delivering therapeutic doses in reasonable exposure times. The proposed collimator consists of two stages, each containing six trapezoidal brass blocks that move along a frame in a manner similar to a camera iris producing a hexagonal aperture of variable size. The two stages are offset by 30 degrees and adjusted for the divergence of the x-ray beam so as to produce a dodecagonal profile at isocenter. Slotted rotating driving plates are used to apply force to pins in the collimator blocks and effect collimator motion. This device has been investigated through both simulation and measurement. The collimator aperture size varied from 0 to 8.5 cm as the driving plate angle increased from 0 to 41 degrees. The torque required to adjust the collimator varied from 0.5 to 5 N x m, increasing with increasing driving plate angle. The transmission profiles produced by the scanner at isocenter exhibited a penumbra of approximately 10% of the collimator aperture width. Misalignment between the collimator assembly and the x-ray source could be identified on the transmission images and corrected by adjustment of the collimator location. This variable aperture collimator technology is therefore a feasible and flexible solution for adjustable shaping of radiation beams for use in small animal radiotherapy as well as other applications in which beam shaping is desired.
一般来说，对小动物进行放射治疗时，辐射仅限于用铅块塑形的平面野，这使得剂量的空间定位以及深部靶标的治疗变得复杂。为了使实验室放疗向临床放疗的水平迈进，我们构建了一种可变孔径准直器，用于对微型CT扫描仪的光束进行塑形。该装置能够以高分辨率对小动物进行成像，并且能够在合理的照射时间内提供治疗剂量。所提出的准直器由两级组成，每级包含六个梯形黄铜块，这些黄铜块沿着框架移动，其方式类似于相机光圈，可产生大小可变的六边形孔径。两级相互错开30度，并针对X射线束的发散进行调整，以便在等中心处产生十二边形轮廓。开槽的旋转驱动板用于向准直器块中的销施加力并实现准直器的运动。该装置已通过模拟和测量进行了研究。随着驱动板角度从0度增加到41度，准直器孔径尺寸从0变化到8.5厘米。调整准直器所需的扭矩从0.5变化到5牛·米，随驱动板角度的增加而增大。扫描仪在等中心处产生的透射轮廓显示半值宽度约为准直器孔径宽度的10%。准直器组件与X射线源之间的不对准可以在透射图像上识别出来，并通过调整准直器位置进行校正。因此，这种可变孔径准直器技术是一种可行且灵活的解决方案，可用于小动物放射治疗以及其他需要光束塑形的应用中对辐射束进行可调塑形。
