Jursinic Paul A, Nelms Ben E
Medical College of Wisconsin, Radiation Oncology Department, Milwaukee, Wisconsin 53792, USA.
Med Phys. 2003 May;30(5):870-9. doi: 10.1118/1.1567831.
An analysis is made of a two-dimensional array of diodes that can be used for measuring dose generated in a plane by a radiation beam. This measuring device is the MapCHECK Model 1175 (Sun Nuclear, Melbourne, FL). This device has 445 N-type diodes in a 22 x 22 cm2 2-D array with variable spacing. The entire array of diodes is easily calibrated to allow for measurements in absolute dose. For IMRT quality assurance, each beam is measured individually with the beam central axis oriented perpendicular to the plane of diodes. Software is available to do the analytical comparison of measurements versus dose distributions calculated by a treatment planning system. Comparison criteria of percent difference and distance-to-agreement are defined by the operator. Data are presented that show the diode array has linear response when beam fluence changes by over 300-fold, which is typical of the level of modulation in intensity modulated radiation therapy, IMRT, beams. A linear dependence is also shown for a 100-fold change in monitors units delivered. Methods for how this device can be used in the clinic for quality assurance of IMRT fields are described. Measurements of typical IMRT beams that are modulated by compensators and MLCs are presented with comparisons to treatment planning system dose calculations. A time analysis is done for typical IMRT quality assurance measurements. The setup, calibration, and analysis time for the 2-D diode array are on the order of 20 min, depending on numbers of fields. This is significantly less time than required to do similar analysis with radiographic film. The 2-D diode array is ideal for per-plan quality assurance after an IMRT system is fully commissioned.
对可用于测量辐射束在平面中产生的剂量的二维二极管阵列进行了分析。这种测量设备是MapCHECK型号1175（佛罗里达州墨尔本的Sun Nuclear公司）。该设备在一个22×22平方厘米的二维阵列中有445个N型二极管，间距可变。整个二极管阵列易于校准，以进行绝对剂量测量。对于调强放射治疗（IMRT）的质量保证，每个射束都单独测量，射束中心轴垂直于二极管平面。有软件可用于对测量值与治疗计划系统计算的剂量分布进行分析比较。百分比差异和一致性距离的比较标准由操作人员定义。给出的数据表明，当射束注量变化超过300倍时，二极管阵列具有线性响应，这是调强放射治疗（IMRT）射束中典型的调制水平。对于输送的监测单位变化100倍的情况，也显示出线性相关性。描述了该设备如何在临床中用于IMRT射野质量保证的方法。给出了由补偿器和多叶准直器调制的典型IMRT射束的测量结果，并与治疗计划系统的剂量计算结果进行了比较。对典型的IMRT质量保证测量进行了时间分析。二维二极管阵列的设置、校准和分析时间约为20分钟，具体取决于射野数量。这比使用射线照相胶片进行类似分析所需的时间要少得多。二维二极管阵列非常适合在IMRT系统完全调试后进行每个计划的质量保证。
