Feng Yuanming, Allison Ron, Hu Xin-Hua, Mota Helvecio, Jenkins Todd, Wolfe Melodee L, Sibata Claudio
Department of Radiation Oncology, The Brody School of Medicine, East Carolina University, Greenville, NC, USA.
Int J Radiat Oncol Biol Phys. 2005 Apr 1;61(5):1587-9. doi: 10.1016/j.ijrobp.2004.12.021.
To develop an ultrasound-based source to skin surface distance (SSD) measurement technique and device for patient setup and test its feasibility and accuracy.
The ultrasonic SSD measurement device (USD) prototype consists of two main parts: a probe plate with an ultrasonic transducer in the center and a control unit that displays the SSD in millimeters. The probe plate can be slid into the block tray accessory slot of any treatment machine at the time of the SSD measurement. The probe plate contains an ultrasonic transducer as both the source and the detector for measuring the distance between the transducer and the target surfaces on the basis of an echo-detecting technique. The device was calibrated by a mechanical ruler with an accuracy of 0.01 mm and corrected by an offset of 601.7 mm, which is the distance from the radiation source to the ultrasonic transducer surface for the Siemens Primus linear accelerator (Linac). The ultrasound device provided digital readout with an accuracy of +/-0.1 mm for a flat surface after calibration. The SSD measurement experiments were done with the USD, an optical distance indicator (ODI), and an AKTINA 53-104 Mechanical Front Pointer (FP) on a Siemens Primus Linac with a full-sized female phantom. Ten measurements were carried out at each gantry angle of 0 degrees , 52 degrees , 85 degrees , 90 degrees , and 227 degrees for anatomic locations of head, thorax, breast, and pelvis, to obtain the average values and standard deviations.
The comparison study with the ODI and FP showed that the USD had an accuracy of less than +/-1.0 mm and that USD measurements had the minimum standard deviations among the three methods; therefore, USD gave more consistent and accurate readouts for SSD measurement. When considering the FP as a reference, the USD yields smaller deviations than the ODI for all measured locations (less than +/-2 mm). The variation of USD digital readout with a room temperature change of +/-2 degrees C is +/-0.1 mm, which is sufficiently accurate for SSD measurement.
The USD method has the following advantages. First, it decreases patient setup time by avoiding problems related to the blocking of the device by the patient or by the immobilization device. Second, it is more accurate than the other two methods currently used, as the test data show. Last, the digital readout eliminates the possibility of human reading error associated with the visual scales.
开发一种基于超声的源皮距（SSD）测量技术及装置用于患者摆位，并测试其可行性和准确性。
超声SSD测量装置（USD）原型由两个主要部分组成：一个中心带有超声换能器的探头板和一个以毫米为单位显示SSD的控制单元。在进行SSD测量时，探头板可滑入任何治疗机的模块托盘附件插槽。探头板包含一个超声换能器，其作为源和探测器，基于回波检测技术测量换能器与目标表面之间的距离。该装置通过精度为0.01 mm的机械尺进行校准，并通过601.7 mm的偏移量进行校正，601.7 mm是西门子Primus直线加速器（直线加速器）从辐射源到超声换能器表面的距离。校准后，超声装置对于平面提供精度为±0.1 mm的数字读数。SSD测量实验在配备全尺寸女性体模的西门子Primus直线加速器上使用USD、光学距离指示器（ODI）和AKTINA 53 - 104机械前指针（FP）进行。在0度、52度、85度、90度和227度的每个机架角度下，针对头部、胸部、乳房和骨盆的解剖位置进行了十次测量，以获得平均值和标准差。
与ODI和FP的比较研究表明，USD的精度小于±1.0 mm，并且在三种方法中USD测量的标准差最小；因此，USD在SSD测量中给出了更一致和准确的读数。当将FP作为参考时，对于所有测量位置，USD产生的偏差都比ODI小（小于±2 mm）。USD数字读数随室温±2℃变化的变化量为±0.1 mm，这对于SSD测量来说足够精确。
USD方法具有以下优点。首先，通过避免患者或固定装置对设备造成遮挡的相关问题，减少了患者摆位时间。其次，如测试数据所示，它比目前使用的其他两种方法更准确。最后，数字读数消除了与视觉刻度相关的人为读数误差的可能性。
