Department of Radiation Oncology, School of Medicine, The University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA.
J Appl Clin Med Phys. 2024 Feb;25(2):e14173. doi: 10.1002/acm2.14173. Epub 2023 Oct 19.
The purpose is to reduce normal tissue radiation toxicity for electron therapy through the creation of a surface-conforming electron multileaf collimator (SCEM). The SCEM combines the benefits of skin collimation, electron conformal radiotherapy, and modulated electron radiotherapy. An early concept for the SCEM was constructed. It consists of leaves that protrude towards the patient, allowing the leaves to conform closely to irregular patient surfaces. The leaves are made of acrylic to decrease bremsstrahlung, thereby decreasing the out-of-field dose. Water tank scans were performed with the SCEM in place for various field sizes for all available electron energies (6, 9, 12, and 15 MeV) with a 0.5 cm air gap to the water surface at 100 cm source-to-surface distance (SSD). These measurements were compared with Cerrobend cutouts with the field size-matched at 100 and 110 cm SSD. Output factor measurements were taken in solid water for each energy at d for both the cerrobend cutouts and SCEM at 100 cm SSD. Percent depth dose (PDD) curves for the SCEM shifted shallower for all energies and field sizes. The SCEM also produced a higher surface dose relative to Cerrobend cutouts, with the maximum being a 9.8% increase for the 3 cm × 9 cm field at 9 MeV. When compared to the Cerrobend cutouts at 110 cm SSD, the SCEM showed a significant decrease in the penumbra, particularly for lower energies (i.e., 6 and 9 MeV). The SCEM also showed reduced out-of-field dose and lower bremsstrahlung production than the Cerrobend cutouts. The SCEM provides significant improvement in the penumbra and out-of-field dose by allowing collimation close to the skin surface compared to Cerrobend cutouts. However, the added scatter from the SCEM increases shallow PDD values. Future work will focus on reducing this scatter while maintaining the penumbra and out-of-field benefits the SCEM has over conventional collimation.
目的是通过创建表面贴合电子多叶准直器（SCEM）来降低电子治疗中正常组织的辐射毒性。SCEM 结合了皮肤准直、电子适形放疗和调强电子放疗的优点。SCEM 的早期概念已经构建完成。它由朝向患者突出的叶片组成，使叶片能够紧密贴合不规则的患者表面。叶片由亚克力制成，以减少韧致辐射，从而降低场外剂量。在水水箱中进行了扫描，将 SCEM 放置在各种大小的场中，适用于所有可用的电子能量（6、9、12 和 15 MeV），在距离水表面 100 cm 的源到表面距离（SSD）处有 0.5 cm 的空气间隙。这些测量结果与 Cerrobend 切痕进行了比较，切痕的场大小在 100 和 110 cm SSD 处相匹配。在每个能量下，在固体水中对 Cerrobend 切痕和 SCEM 进行了 100 cm SSD 的 d 处的输出因子测量。对于所有能量和场大小，SCEM 的百分深度剂量（PDD）曲线都变得更浅。SCEM 还产生了比 Cerrobend 切痕更高的表面剂量，在 9 MeV 时，3 cm×9 cm 场的最大增加量为 9.8%。与 110 cm SSD 处的 Cerrobend 切痕相比，SCEM 显示出阴影区域的显著减小，特别是对于较低的能量（即 6 和 9 MeV）。SCEM 还显示出比 Cerrobend 切痕更低的场外剂量和更少的韧致辐射产生。与 Cerrobend 切痕相比，SCEM 通过允许在靠近皮肤表面的地方进行准直，在阴影区域和场外剂量方面提供了显著的改进。然而，SCEM 增加的散射会增加浅层 PDD 值。未来的工作将集中在减少这种散射的同时保持 SCEM 相对于传统准直的阴影区域和场外益处。
