4B02a-Simulator acceptance, commissioning, QA

(a) conventional simulator

(b) CT simulator

James C. H. Chu, PhD

Rush University Medical Center

Chicago, IL  60612

(a) A conventional simulator consists of a patient positioning couch, a rotating gantry, and associated controls. The gantry is mounted with a diagnostic x-ray source and an image intensifier. The simulator is capable of similar gantry and couch movements from a linear accelerator. This capability allows the simulator to perform a “reality check” for the treatment delivery geometry designed by a treatment planning system or from a CT simulator. The reproducibility of the patient position can be verified by diagnostic quality x-ray images; other potential patient setup problems can also be identified before the commencement of treatments. A QA program is necessary to assure that the simulator operates within the mechanical and radiation alignment tolerances expected from a linear accelerator. In addition, the performance of the imaging component requires careful evaluation. For example, the correction of image distortion from the image intensifier is necessary if the images are to be used to design the shape of treatment fields. Some of the simulators provide limited number of CT images. The accuracy of those image should also be verified if they are used for treatment planning or CT-based dose calculations.

4B02a-模拟机验收、试运行、质量保证

(a) 常规模拟机

(b) CT模拟机

James C. H. Chu, PhD

Rush University Medical Center

Chicago, IL  60612

(a) 一台常规的模拟机包括病人定位床、旋转机架和相关的控制装置。机架上装有一个诊断X线源和影像增强器。这种模拟机具有类似加速器的机架和床的运动功能。使得它可以进行治疗计划系统设计的或CT模拟机设计的治疗计划的几何参数的“实际模拟”。病人位置的重复性可以通过诊断X线影像来验证；其它可能的病人摆位问题也可以在治疗开始之前被发现。一套质量保证程序是必要的，以保证模拟机达到和加速器一样的机械和射野大小的精度。另外，影像部分的性能亦需要仔细的评估。例如，当影像用于设计治疗野的形状时，由影像增强而来的影像失真的修正是必需的。有些模拟机会提供有限数目的CT影像。当这些影像用于治疗计划设计或是基于CT的剂量计算时，它们的精确度需要经过验证。