University of Pennsylvania.
J Appl Clin Med Phys. 2014 May 8;15(3):4748. doi: 10.1120/jacmp.v15i3.4748.
Because treatment planning systems (TPSs) generally do not provide monitor units (MUs) for double-scattered proton plans, models to predict MUs as a function of the range and the nominal modulation width requested of the beam delivery system, such as the one developed by the MGH group, have been proposed. For a given nominal modulation width, however, the measured modulation width depends on the accuracy of the vendor's calibration process and may differ from this nominal value, and also from one beamline to the next. Although such a difference can be replicated in our TPS, the output dependence on range and modulation width for each beam option or suboption has to be modeled separately for each beamline in order to achieve maximal 3% inaccuracy. As a consequence, the MGH output model may not be directly transferable. This work, therefore, serves to extend the model to more general clinic situations. In this paper, a parameterized linear-quadratic transformation is introduced to convert the nominal modulation width to the measured modulation width for each beam option or suboption on a per-beamline basis. Fit parameters are derived for each beamline from measurements of 60 reference beams spanning the minimum and maximum ranges, and modulation widths from 2 cm to full range per option or suboption. Using the modeled modulation width, we extract the MGH parameters for the output dependence on range and modulation width. Our method has been tested with 1784 patient-specific fields delivered across three different beamlines at our facility. For these fields, all measured outputs fall within 3%, and 64.4% fall within 1%, of our model. Using a parameterized linear-quadratic modulation width, MU calculation models can be established on a per-beamline basis for each double scattering beam option or suboption.
由于治疗计划系统（TPS）通常不为双散射质子计划提供监测单位（MU），因此已经提出了一些模型来预测 MU，这些模型将 MU 作为束流传输系统的射程和名义调制宽度的函数，例如 MGH 小组开发的模型。然而，对于给定的名义调制宽度，测量的调制宽度取决于供应商校准过程的准确性，并且可能与该名义值以及从一条束线到另一条束线不同。尽管这种差异可以在我们的 TPS 中复制，但对于每个束选项或子选项，输出对射程和调制宽度的依赖性必须分别针对每条束线进行建模，以实现最大 3%的不准确性。因此，MGH 输出模型可能无法直接转移。因此，这项工作旨在将模型扩展到更一般的临床情况。在本文中，引入了参数化的线性二次变换，以便将每个束选项或子选项的名义调制宽度转换为每条束线的测量调制宽度。对于每个束线，从跨越最小和最大射程的 60 个参考束的测量值以及每个选项或子选项的 2cm 至全射程的调制宽度中推导出拟合参数。使用建模的调制宽度，我们提取了 MGH 参数，以表示输出对射程和调制宽度的依赖性。我们的方法已经在我们的设施中的三条不同束线上的 1784 个患者特定场中进行了测试。对于这些场，所有测量的输出都在我们模型的 3%以内，64.4%在 1%以内。使用参数化的线性二次调制宽度，可以为每个双散射束选项或子选项建立每条束线的 MU 计算模型。
