Accuracy of pencil-beam redefinition algorithm dose calculations in patient-like cylindrical phantoms for bolus electron conformal therapy
Accuracy of pencil-beam redefinition algorithm dose calculations in patient-like cylindrical phantoms for bolus electron conformal therapy
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DOI：
10.1118/1.4811104
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发表时间：
2013-07-01
期刊：
影响因子：
3.8
通讯作者：
Sprunger, Conrad P.
中科院分区：
文献类型：
--
作者：
Carver, Robert L.;Hogstrom, Kenneth R.;Sprunger, Conrad P.
目的：本研究的目的是记录笔形射束重定义算法（PBRA）与笔形射束算法（PBA）相比，使用基于磨牙后三角区和鼻癌患者计算机断层扫描（CT）的圆柱形患者体模进行团注电子适形治疗的准确性提高。方法：PBRA和PBA的电子剂量计算与测量的剂量在磨牙后三角区和鼻模型进行了比较，有和没有团注。对于团注治疗计划，放射肿瘤学家在每个体模的CT扫描的中心轴切片上概述了计划靶体积（PTV）。使用planning.decimal（R）（p.d）软件（. decimal，Inc.，Sanford，FL），以使90%剂量线与PTV的远端表面一致。将热释光剂量计放入预钻孔中进行剂量测量。使用Pinnacle（3）（Philips Healthcare，Andover，MD）治疗计划系统计算PBA剂量分布。使用内部C++程序计算PBRA剂量分布。为了准确说明体模材料，编制了一个将CT数与相对电子阻止和散射功率相关联的表格，并用于PBA和PBRA剂量计算。通过比较测量和计算剂量的差异，以及每个测量点的距离来确定准确度：测量剂量的平均精度为0.9%。对于磨牙后三角体模，PBRA剂量计算的平均+/- 1 sigma剂量差（计算-测量）为-0.65% +/- 1.62%（无推注）和-0.20% +/- 1.54%（有推注）。PBA剂量计算的平均剂量差异为0.19% +/- 3.27%（无推注）和-0.05% +/- 3.14%（有推注）。对于鼻部体模，PBRA剂量计算的平均剂量差异为0.50% +/- 3.06%（无推注）和-0.18% +/- 1.22%（有推注）。PBA剂量计算的平均剂量差异为0.65% +/- 6.21%（无推注）和1.75% +/- 5.94%（有推注）。从临床角度来看，计划（计算）和输送（测量）剂量之间的一致性需要达到5%或更高。从统计学上讲，PBRA剂量计算的四种情况中有三种情况的99%（+/- 2 σ）的剂量点是正确的，但无推注的鼻子除外，其89%（+/- 1.6 σ）的剂量点是正确的。对于磨牙后三角区，在有和没有推注的情况下，PBA显示约86%（+/- 1.5 sigma）的剂量点的一致性为5%或更好。对于鼻子，有和没有团，PBA显示协议的5%或更好的只有大约58%（+/- 0.8西格玛）的剂量points.Conclusions：测量数据，其高精度，使他们有用的电子剂量算法的准确性评估，将公开提供。基于剂量差异的分布，PBRA的准确度至少是PBA的两倍。从临床角度来看，在磨牙后三角区和鼻部进行电子治疗（有或无团注）时，PBRA准确性是可以接受的。(C)2013年美国医学物理学家协会。
Purpose: The purpose of this study was to document the improved accuracy of the pencil beam redefinition algorithm (PBRA) compared to the pencil beam algorithm (PBA) for bolus electron conformal therapy using cylindrical patient phantoms based on patient computed tomography (CT) scans of retromolar trigone and nose cancer.Methods: PBRA and PBA electron dose calculations were compared with measured dose in retromolar trigone and nose phantoms both with and without bolus. For the bolus treatment plans, a radiation oncologist outlined a planning target volume (PTV) on the central axis slice of the CT scan for each phantom. A bolus was designed using the planning.decimal (R) (p.d) software (. decimal, Inc., Sanford, FL) to conform the 90% dose line to the distal surface of the PTV. Dose measurements were taken with thermoluminescent dosimeters placed into predrilled holes. The Pinnacle(3) (Philips Healthcare, Andover, MD) treatment planning system was used to calculate PBA dose distributions. The PBRA dose distributions were calculated with an in-house C++ program. In order to accurately account for the phantom materials a table correlating CT number to relative electron stopping and scattering powers was compiled and used for both PBA and PBRA dose calculations. Accuracy was determined by comparing differences in measured and calculated dose, as well as distance to agreement for each measurement point.Results: The measured doses had an average precision of 0.9%. For the retromolar trigone phantom, the PBRA dose calculations had an average +/- 1 sigma dose difference (calculated - measured) of -0.65% +/- 1.62% without the bolus and -0.20% +/- 1.54% with the bolus. The PBA dose calculation had an average dose difference of 0.19% +/- 3.27% without the bolus and -0.05% +/- 3.14% with the bolus. For the nose phantom, the PBRA dose calculations had an average dose difference of 0.50% +/- 3.06% without bolus and -0.18% +/- 1.22% with the bolus. The PBA dose calculations had an average dose difference of 0.65% +/- 6.21% without bolus and 1.75% +/- 5.94% with the bolus. From a clinical perspective an agreement of 5% or better between planned (calculated) and delivered (measured) dose is desired. Statistically, this was true for 99% (+/- 2 sigma) of the dose points for three of the four cases for the PBRA dose calculations, the exception being the nose without bolus for which this was true for 89% (+/- 1.6 sigma) of the dose points. For the retromolar trigone, with and without bolus, the PBA showed agreement of 5% or better for approximately 86% (+/- 1.5 sigma) of the dose points. For the nose, with and without bolus, the PBA showed agreement of 5% or better for only approximately 58% (+/- 0.8 sigma) of the dose points.Conclusions: The measured data, whose high precision makes them useful for evaluation of the accuracy of electron dose algorithms, will be made publicly available. Based on the spread in dose differences, the PBRA has at least twice the accuracy of the PBA. From a clinical perspective the PBRA accuracy is acceptable in the retromolar trigone and nose for electron therapy with and without bolus. (C) 2013 American Association of Physicists in Medicine.