Department of Medical Physics, Hospital Sant Joan de Reus, IISPV, 43204 Tarragona, Spain.
Phys Med Biol. 2018 Dec 10;63(24):245005. doi: 10.1088/1361-6560/aaf098.
Commercial TPSs typically model the tongue-and-groove (TG) by extending the projections of the leaf sides by a certain constant width. However, this model may produce discrepancies of as much as 7%-10% in the calculated average doses, especially for the High Definition multi-leaf collimator (MLC) (Hernandez et al 2017 Phys. Med. Biol. 62 6688-707). The purpose of the present study is to introduce and validate a new method for modelling the TG that uses a non constant TG width. We provide the theoretical background and a detailed methodology to determine the optimal shape of this TG width from measurements and we fit an empirical function to the TG width that depended on two parameters [Formula: see text] and [Formula: see text]. Parameter [Formula: see text] represents the TG width and [Formula: see text] introduces a curvature correction in the width near the leaf tip end. The new TG model was implemented in MATLAB and when the curvature correction was zero ([Formula: see text]) it caused the same discrepancies as the constant width model used by the Eclipse TPS. On the other hand, when the experimentally determined [Formula: see text] was used the new model's calculations were in close agreement with measurements, with all differences in average doses [Formula: see text]1%. Additionally, film dosimetry was used to successfully validate the potential of the new TG model to recreate the fine spatial details associated to TG effects. We also showed that the parameters [Formula: see text], [Formula: see text] depend solely on the MLC design by evaluating three different linear accelerators for each MLC model considered, namely Varian's High Definition and Millennium120 MLCs. In conclusion, a new method was presented that greatly improves the TG modelling. The present method can be easily implemented in commercial TPSs and has the potential to further increase their accuracy, especially for MLCs with rounded leaf ends.
商业束流调强系统（TPS）通常通过将叶片边缘的突出部分向外延伸一定的恒定宽度来模拟凹凸槽（TG）。然而，这种模型可能会导致计算出的平均剂量产生高达 7%-10%的差异，特别是对于高解析度多叶准直器（MLC）（Hernandez 等人，2017 年，《物理医学与生物学》，第 62 卷，第 6688-707 页）。本研究的目的是引入并验证一种新的 TG 建模方法，该方法使用非恒定的 TG 宽度。我们提供了理论背景和详细的方法，从测量中确定这种 TG 宽度的最佳形状，并拟合一个经验函数到 TG 宽度，该函数取决于两个参数 [公式：见文本] 和 [公式：见文本]。参数 [公式：见文本] 代表 TG 宽度，[公式：见文本] 在叶片尖端附近的宽度中引入曲率修正。新的 TG 模型在 MATLAB 中实现，当曲率修正为零时（[公式：见文本]），它会导致与 Eclipse TPS 使用的恒定宽度模型相同的差异。另一方面，当使用实验确定的 [公式：见文本] 时，新模型的计算结果与测量结果非常吻合，所有平均剂量的差异都在 [公式：见文本]1%以内。此外，使用胶片剂量测定法成功验证了新 TG 模型重现与 TG 效应相关的精细空间细节的潜力。我们还表明，参数 [公式：见文本]、[公式：见文本] 仅取决于 MLC 设计，通过评估每个考虑的 MLC 模型的三种不同的直线加速器，即瓦里安的高解析度和 Millennium120 MLC。总之，提出了一种大大改进 TG 建模的新方法。该方法可以很容易地在商业 TPS 中实现，并有可能进一步提高它们的准确性，特别是对于叶片末端为圆形的 MLC。
