Department of Radiation Physics, the University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.
Med Phys. 2013 May;40(5):051710. doi: 10.1118/1.4802216.
The novel deterministic radiation transport algorithm, Acuros XB (AXB), has shown great potential for accurate heterogeneous dose calculation. However, the clinical impact between AXB and other currently used algorithms still needs to be elucidated for translation between these algorithms. The purpose of this study was to investigate the impact of AXB for heterogeneous dose calculation in lung cancer for intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT).
The thorax phantom from the Radiological Physics Center (RPC) was used for this study. IMRT and VMAT plans were created for the phantom in the Eclipse 11.0 treatment planning system. Each plan was delivered to the phantom three times using a Varian Clinac iX linear accelerator to ensure reproducibility. Thermoluminescent dosimeters (TLDs) and Gafchromic EBT2 film were placed inside the phantom to measure delivered doses. The measurements were compared with dose calculations from AXB 11.0.21 and the anisotropic analytical algorithm (AAA) 11.0.21. Two dose reporting modes of AXB, dose-to-medium in medium (Dm,m) and dose-to-water in medium (Dw,m), were studied. Point doses, dose profiles, and gamma analysis were used to quantify the agreement between measurements and calculations from both AXB and AAA. The computation times for AAA and AXB were also evaluated.
For the RPC lung phantom, AAA and AXB dose predictions were found in good agreement to TLD and film measurements for both IMRT and VMAT plans. TLD dose predictions were within 0.4%-4.4% to AXB doses (both Dm,m and Dw,m); and within 2.5%-6.4% to AAA doses, respectively. For the film comparisons, the gamma indexes (± 3%∕3 mm criteria) were 94%, 97%, and 98% for AAA, AXB_Dm,m, and AXB_Dw,m, respectively. The differences between AXB and AAA in dose-volume histogram mean doses were within 2% in the planning target volume, lung, heart, and within 5% in the spinal cord. However, differences up to 8% between AXB and AAA were found at lung∕soft tissue interface regions for individual IMRT fields. AAA was found to be 5-6 times faster than AXB for IMRT, while AXB was 4-5 times faster than AAA for VMAT plan.
AXB is satisfactorily accurate for the dose calculation in lung cancer for both IMRT and VMAT plans. The differences between AXB and AAA are generally small except in heterogeneous interface regions. AXB Dw,m and Dm,m calculations are similar inside the soft tissue and lung regions. AXB can benefit lung VMAT plans by both improving accuracy and reducing computation time.
新型确定性辐射传输算法 Acuros XB（AXB）在精确计算不均匀剂量方面显示出巨大潜力。然而，为了在这些算法之间进行转换，仍需要阐明 AXB 与其他当前使用的算法之间的临床差异。本研究旨在探讨 AXB 在肺癌调强放疗（IMRT）和容积调强弧形治疗（VMAT）中的不均匀剂量计算中的影响。
本研究使用放射物理中心（RPC）的体模。在 Eclipse 11.0 治疗计划系统中为体模创建了 IMRT 和 VMAT 计划。每个计划都使用瓦里安 Clinac iX 线性加速器三次输送到体模中，以确保可重复性。热释光剂量计（TLD）和 Gafchromic EBT2 胶片被放置在体模内以测量输送剂量。将测量结果与 AXB 11.0.21 和各向异性分析算法（AAA）11.0.21 的剂量计算进行比较。研究了 AXB 的两种剂量报告模式，即介质中的剂量到介质（Dm,m）和介质中的剂量到水（Dw,m）。使用点剂量、剂量分布和伽马分析来量化 AXB 和 AAA 测量值和计算值之间的一致性。还评估了 AAA 和 AXB 的计算时间。
对于 RPC 肺部体模，AAA 和 AXB 的剂量预测与 TLD 和胶片测量结果在 IMRT 和 VMAT 计划中均具有良好的一致性。TLD 剂量预测与 AXB 剂量（Dm,m 和 Dw,m）的偏差在 0.4%-4.4%之间；与 AAA 剂量的偏差分别在 2.5%-6.4%之间。对于胶片比较，AAA、AXB_Dm,m 和 AXB_Dw,m 的伽马指数（±3%/3mm 标准）分别为 94%、97%和 98%。AXB 和 AAA 在计划靶区、肺、心脏和脊髓的剂量体积直方图平均剂量上的差异均在 2%以内，而在肺部/软组织界面区域的个体 IMRT 场中，差异高达 8%。对于个体 IMRT 场，在肺部/软组织界面区域发现 AXB 与 AAA 之间的差异高达 8%。对于 IMRT，AAA 比 AXB 快 5-6 倍，而对于 VMAT 计划，AXB 比 AAA 快 4-5 倍。
AXB 在 IMRT 和 VMAT 计划中用于肺癌剂量计算时具有令人满意的准确性。除了不均匀界面区域外，AXB 和 AAA 之间的差异通常较小。AXB 在软组织和肺部区域内的 Dw,m 和 Dm,m 计算结果相似。AXB 可以通过提高准确性和减少计算时间来受益于肺部 VMAT 计划。
