Department of Radiation Oncology, Henry Ford Health System, Detroit, MI, USA.
J Appl Clin Med Phys. 2019 Aug;20(8):87-97. doi: 10.1002/acm2.12682. Epub 2019 Jul 22.
The AeroForm chest wall tissue expander (TE) is a silicon shell containing a metallic CO reservoir, placed surgically after mastectomy. The patient uses a remote control to release compressed CO from the reservoir to inflate the expander. AeroForm poses challenges in a radiation therapy setting: The high density of the metallic reservoir causes imaging artifacts on the planning CT, which encumber structure definition and cause misrepresentation of density information, in turn affecting dose calculation. Additionally, convolution-based dose calculation algorithms may not be well-suited to calculate dose in and around high-density materials. In this study, a model of the AeroForm TE was created in Eclipse treatment planning system (TPS). The TPS model was validated by comparing measured to calculated transmission through the AeroForm. Transmission was measured with various geometries using radiochromic film. Dose was calculated with both Varian's Anisotropic Analytical Algorithm (AAA) and Acuros External Beam (AXB) algorithms. AAA and AXB were compared using dose profile and gamma analyses. While both algorithms modeled direct transmission well, AXB better modeled lateral scatter from the AeroForm TE. Clinical significance was evaluated using clinical data from four patients with AeroForm TEs. The AeroForm TPS model was applied, and RT plans were optimized using AAA, then re-calculated with AXB. Structures of clinical significance were defined and dose volume histogram analysis was performed. Compared to AXB, AAA overestimates dose in the AeroForm device. Changes in clinically significant regions were patient- and plan-specific. This study proposes a clinical procedure for modeling the AeroForm in a commercial TPS, and discusses the limitations of dose calculation in and around the device. An understanding of dose calculation accuracy in the vicinity of the AeroForm is critical for assessing individual plan quality, appropriateness of different planning techniques and dose calculation algorithms, and even the decision to use the AeroForm in a postmastectomy radiation therapy setting.
AeroForm 胸廓组织扩张器（TE）是一种硅壳，内部包含一个金属 CO 储库，在乳房切除术后进行手术放置。患者使用遥控器将储库中的压缩 CO 释放出来，使扩张器充气。AeroForm 在放射治疗环境中带来了挑战：金属储库的高密度在计划 CT 上导致成像伪影，这妨碍了结构定义并导致密度信息的错误表示，进而影响剂量计算。此外，基于卷积的剂量计算算法可能不适合计算高密度材料内部和周围的剂量。在这项研究中，在 Eclipse 治疗计划系统（TPS）中创建了 AeroForm TE 的模型。通过比较通过 AeroForm 的测量和计算的透射率来验证 TPS 模型。使用放射色胶片测量了各种几何形状的透射率。使用瓦里安的各向异性分析算法（AAA）和 Acuros 外部束（AXB）算法计算剂量。使用剂量分布和伽马分析比较了 AAA 和 AXB。虽然这两种算法都很好地模拟了直接传输，但 AXB 更好地模拟了来自 AeroForm TE 的侧向散射。使用来自四名患有 AeroForm TE 的患者的临床数据评估了临床意义。应用了 AeroForm TPS 模型，并使用 AAA 优化了 RT 计划，然后使用 AXB 重新计算。定义了具有临床意义的结构，并进行了剂量体积直方图分析。与 AXB 相比，AAA 高估了 AeroForm 装置中的剂量。在具有临床意义的区域中发生的变化因患者和计划而异。本研究提出了一种在商业 TPS 中对 AeroForm 进行建模的临床程序，并讨论了在设备内部和周围进行剂量计算的局限性。了解 AeroForm 附近的剂量计算准确性对于评估单个计划质量、不同计划技术和剂量计算算法的适用性以及甚至决定在乳房切除术后放射治疗环境中使用 AeroForm 都至关重要。
