Bush K, Wang L, Mok E
Stanford University Cancer Center, Palo Alto, CA.
Med Phys. 2012 Jun;39(6Part17):3816-3817. doi: 10.1118/1.4735574.
The Acuros XB (AXB) Advanced Dose algorithm (Varian Medical Systems) represents a dramatic shift in clinical photon dose calculation methodology from pencil-beam superposition/convolution methods. Early studies evaluating the accuracy of the algorithm in lung have found good agreement with both measurement and Monte Carlo based dose calculations. In this study, a dosimetric validation of Acuros is performed for clinical SBRT lung planning cases using Monte Carlo (MC) calculations as a benchmark.
MC simulations using BEAMnrc/DOSXYZnrc were carried out for 8 AXB calculated 6/10 MV arc plans delivered on a TrueBeamTM STx linac in high-dose-rate flattening filter free mode. Clinical planning constraints were applied in each case with plans normalized to achieve 95% PTV coverage. Metrics used in the evaluation include: maximum and minimum GTV/PTV dose, PTV isodose coverage, conformity and dose profile comparisons. To understand the impact of moving toward to AXB calculations in SBRT lung planning, calculations using the Analytical Anisotropic Algorithm (AAA) are presented for each plan.
For both 6 and 10MV energies, consistent mean GTV dose and PTV isodose coverage was observed for AXB and MC calculations. GTV mean dose was observed to deviate by <2% for all cases. Isodose coverage for MC simulations ranged from 92%-98%. AAA was also in agreement with MC simulations within the GTV to within 2%. AXB and MC maximum and minimum PTV dose differences were larger (up to 9%) but not of clinical concern. In several cases, AXB exhibited a significant improvement in dose calculation accuracy in the lung region surrounding the GTV over AAA, particularly with lung densities < 0.1 g/cc.
AcurosXB provides increased accuracy in modelling dose deposition for SBRT lung over AAA and is found to be in good agreement with MC calculations.
Acuros XB（AXB）高级剂量算法（瓦里安医疗系统公司）代表了临床光子剂量计算方法从笔形束叠加/卷积方法的重大转变。早期评估该算法在肺部准确性的研究发现，其与测量值以及基于蒙特卡罗的剂量计算结果具有良好的一致性。在本研究中，以蒙特卡罗（MC）计算为基准，对临床SBRT肺部计划病例进行了Acuros的剂量学验证。
使用BEAMnrc/DOSXYZnrc进行MC模拟，针对在TrueBeamTM STx直线加速器上以高剂量率无均整器模式交付的8个AXB计算的6/10 MV弧形计划。每种情况下均应用临床计划约束条件，计划归一化以实现95%的PTV覆盖。评估中使用的指标包括：GTV/PTV的最大和最小剂量、PTV等剂量线覆盖、适形度以及剂量分布比较。为了解在SBRT肺部计划中转向AXB计算的影响，给出了每个计划使用解析各向异性算法（AAA）的计算结果。
对于6 MV和10 MV能量，AXB和MC计算均观察到一致的平均GTV剂量和PTV等剂量线覆盖。所有病例中GTV平均剂量偏差均<2%。MC模拟的等剂量线覆盖范围为92% - 98%。AAA在GTV范围内与MC模拟的一致性也在2%以内。AXB和MC的PTV最大和最小剂量差异较大（高达9%），但不具有临床相关性。在一些病例中，AXB在GTV周围肺部区域的剂量计算准确性方面比AAA有显著提高，尤其是在肺密度<0.1 g/cc时。
与AAA相比，AcurosXB在SBRT肺部剂量沉积建模方面提供了更高的准确性，并且与MC计算结果具有良好的一致性。
