Commissioning dose computation models for spot scanning proton beams in water for a commercially available treatment planning system
Commissioning dose computation models for spot scanning proton beams in water for a commercially available treatment planning system
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DOI：
10.1118/1.4798229
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发表时间：
2013-04-01
期刊：
影响因子：
3.8
通讯作者：
Sahoo, N.
中科院分区：
文献类型：
--
作者：
Zhu, X. R.;Poenisch, F.;Sahoo, N.
目的：介绍在商业化治疗计划系统（TPS）中调试点扫描质子治疗水中剂量模型的方法和经验。方法：TPS所需的输入数据包括空气中横向剖面和积分深度剂量（IDDs）。所有输入数据均来自已通过测量验证的Monte Carlo（MC）模拟。使用最大的市售平行板电离室，在2 cm深度处测量IDD，将MC产生的IDD转换为单位戈伊mm（2）/MU。电离室的敏感区域不足以完全涵盖笔形射束（点）在深度处沉积的整个横向剂量。为了校正探测器尺寸，使用MC定义并确定作为质子能量函数的校正因子。单个光斑的注量最初被建模为单高斯（SG）函数，后来被建模为双高斯（DG）函数。DG注量模型被引入到占点注量由于大角度散射的贡献，从扫描喷嘴内的设备，特别是从点轮廓监视器。为了验证DG注量模型，我们比较了计算和测量，包括在中心的分散布拉格峰（SOBP）的名义字段大小，范围和SOBP宽度，横向剂量分布，和深度剂量的函数为不同宽度的SOBP的剂量。剂量模型进行了验证，广泛与患者治疗领域的具体measurement.Results：我们证明了DG注量模型是必要的剂量分布预测领域的大小依赖。使用该模型，计算的剂量在SOBP中心作为标称字段大小的函数，范围，和SOBP宽度，横向剂量分布和深度剂量的矩形靶体积同意以及与各自的测量值。我们的扫描质子束线的DG通量模型，我们成功地治疗了500多名患者从2010年3月至2012年6月与TPS计算和测量的剂量分布之间的可接受的协议。然而，目前的剂量模型仍然有局限性，在预测字段大小依赖的剂量在一些中间深度的质子束高energy.Conclusions：我们已经委托DG注量模型用于临床使用。它表明，DG通量模型是显着更准确的比SG通量模型。然而，目前的剂量算法在低剂量包络建模方面仍存在一些不足。需要进一步改进当前的剂量算法。这里提出的方法应该是有用的调试笔形束剂量算法在新版本的TPS在未来。(C)2013年美国医学物理学家协会。[http：//dx.doi.org/10.1118/1.4798229]
Purpose: To present our method and experience in commissioning dose models in water for spot scanning proton therapy in a commercial treatment planning system (TPS).Methods: The input data required by the TPS included in-air transverse profiles and integral depth doses (IDDs). All input data were obtained from Monte Carlo (MC) simulations that had been validated by measurements. MC-generated IDDs were converted to units of Gy mm(2)/MU using the measured IDDs at a depth of 2 cm employing the largest commercially available parallel-plate ionization chamber. The sensitive area of the chamber was insufficient to fully encompass the entire lateral dose deposited at depth by a pencil beam (spot). To correct for the detector size, correction factors as a function of proton energy were defined and determined using MC. The fluence of individual spots was initially modeled as a single Gaussian (SG) function and later as a double Gaussian (DG) function. The DG fluence model was introduced to account for the spot fluence due to contributions of large angle scattering from the devices within the scanning nozzle, especially from the spot profile monitor. To validate the DG fluence model, we compared calculations and measurements, including doses at the center of spread out Bragg peaks (SOBPs) as a function of nominal field size, range, and SOBP width, lateral dose profiles, and depth doses for different widths of SOBP. Dose models were validated extensively with patient treatment field-specific measurements.Results: We demonstrated that the DG fluence model is necessary for predicting the field size dependence of dose distributions. With this model, the calculated doses at the center of SOBPs as a function of nominal field size, range, and SOBP width, lateral dose profiles and depth doses for rectangular target volumes agreed well with respective measured values. With the DG fluence model for our scanning proton beam line, we successfully treated more than 500 patients from March 2010 through June 2012 with acceptable agreement between TPS calculated and measured dose distributions. However, the current dose model still has limitations in predicting field size dependence of doses at some intermediate depths of proton beams with high energies.Conclusions: We have commissioned a DG fluence model for clinical use. It is demonstrated that the DG fluence model is significantly more accurate than the SG fluence model. However, some deficiencies in modeling the low-dose envelope in the current dose algorithm still exist. Further improvements to the current dose algorithm are needed. The method presented here should be useful for commissioning pencil beam dose algorithms in new versions of TPS in the future. (C) 2013 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4798229]