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首页> 外文期刊>Medical Physics >On the use of the absorbed depth‐dose measurements in the beam calibration of a surface electronic high‐dose‐rate brachytherapy unit, a Monte Carlo‐based study
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On the use of the absorbed depth‐dose measurements in the beam calibration of a surface electronic high‐dose‐rate brachytherapy unit, a Monte Carlo‐based study

机译：关于使用吸收的深度剂量测量在表面电子高剂量速率近距离放射治疗单元的光束校准中，蒙特卡罗基研究

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Purpose To evaluate the use of the absorbed depth‐dose as a surrogate of the half‐value layer in the calibration of a high‐dose‐rate electronic brachytherapy (eBT) equipment. The effect of the manufacturing tolerances and the absorbed depth‐dose measurement uncertainties in the calibration process are also addressed. Methods The eBT system Esteya ? (Elekta Brachytherapy, Veenendaal, The Netherlands) has been chosen as a proof‐of‐concept to illustrate the feasibility of the proposed method, using its 10?mm diameter applicator. Two calibration protocols recommended by the AAPM (TG‐61) and the IAEA (TRS‐398) for low‐energy photon beams were evaluated. The required Monte Carlo (MC) simulations were carried out using PENELOPE2014. Several MC simulations were performed modifying the flattening filter thickness and the x‐ray tube potential, generating one absorbed depth‐dose curve and a complete set of parameters required in the beam calibration (i.e., HVL, backscatter factor ( B w ), and mass energy‐absorption coefficient ratios (μ en / ρ ) water,air ), for each configuration. Fits between each parameter and some absorbed dose‐ratios calculated from the absorbed depth‐dose curves were established. The effect of the manufacturing tolerances and the absorbed dose‐ratio uncertainties over the calibration process were evaluated by propagating their values over the fitting function, comparing the overall calibration uncertainties against reference values. We proposed four scenarios of uncertainty (from 0% to 10%) in the dose‐ratio determination to evaluate its effect in the calibration process. Results The manufacturing tolerance of the flattening filter (±0.035?mm) produces a change of 1.4% in the calculated HVL and a negligible effect over the B w , (μ en / ρ ) water,air , and the overall calibration uncertainty. A potential variation of 14% of the electron energies due to manufacturing tolerances in the x‐ray tube (69.5?±?~10?keV) generates a variation of 10% in the HVL. However, this change has a negligible effect over the B w and (μ en / ρ ) water,air , adding 0.1% to the overall calibration uncertainty. The fitting functions reproduce the data with an uncertainty ( k ?=?2) below 1%, 0.5%, and 0.4% for the HVL, B w , and (μ en / ρ ) water,air , respectively. The four studied absorbed dose‐ratio uncertainty scenarios add, in the worst‐case scenario, 0.2% to the overall uncertainty of the calibration process. Conclusions This work shows the feasibility of using the absorbed depth‐dose curve in the calibration of an eBT system with minimal loss of precision.
机译：目的，在校准高剂量速率电子近距离放射治疗（EBT）设备时，评估使用吸收的深度剂量作为半值层的替代。还解决了校准过程中的制造公差和吸收的深度剂量测量不确定性的影响。方法EBT系统esteya吗？ （Elekta Brachytherapy，Veenendaal，荷兰）被选为概念验证，以说明使用其10毫米直径施加器的提出方法的可行性。评估了由AAPM（TG-61）和IAEA（TRS-398）推荐用于低能量光子束的校准协议。使用Penelope2014进行所需的蒙特卡罗（MC）模拟。进行几种MC模拟修改扁平化过滤器厚度和X射线管电位，产生一个吸收的深度剂量曲线和光束校准中所需的一组完整的参数（即，HVL，反向散射因子（B W）和质量每个配置的能量吸收系数比（μEN/ρ）水，空气）。建立了从吸收的深度剂曲线计算的每个参数和一些吸收剂量比之间的拟合。通过在装配函数上传播它们的值来评估制造公差和吸收的剂量比不确定性的影响，并将整体校准不确定因素与参考值进行比较来评估校准过程。我们提出了在剂量比测定中的四种不确定性（0％至10％）的情况，以评估其在校准过程中的效果。结果扁平滤波器（±0.035Ωmm）的制造公差在计算的HVL中产生1.4％的变化，以及对B W，（μEN/ρ）水，空气和整体校准不确定的忽略效果。由于X射线管中的制造公差（69.5？±〜10？kev）的制造公差，14％的电能变化产生了HVL中10％的变化。然而，这一变化对B W和（μS/ρ）水，空气的效果可忽略不计，增加0.1％，以整体校准不确定性。拟合功能将具有低于1％，0.5％和0.4％的不确定度（K≤=Δ2）的数据分别再现为HV1，B W和（μEn/ρ）水，空气。在最坏情况的情况下，四所研究的吸收剂量比不确定性情景加入了校准过程的总体不确定性的0.2％。结论这项工作表明，在校准EBT系统中使用吸收的深度剂量曲线的可行性，具有最小的精度损失。

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