Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA.
Med Phys. 2019 Sep;46(9):4087-4094. doi: 10.1002/mp.13706. Epub 2019 Jul 31.
Motion management is critical for the efficacy of carbon ion therapy for moving targets such as lung tumors. We evaluated the feasibility of using four-dimensional cone beam computed tomography (4D-CBCT) reconstructed by Simultaneous Motion Estimation and Image Reconstruction (SMEIR) for dose calculation and accumulation in carbon ion treatment of lung cancer.
Motion-compensated 4D-CBCT images were reconstructed with the SMEIR algorithm to capture the most updated anatomy and motion with an updated interphase motion model on the treatment day. Projections of all CBCT phases were simulated from the planning 4D-CT by the ray tracing technique. Treatment planning and dose calculation were performed with a GPU-based Monte Carlo dose calculation software for carbon ion therapy. The treatment plan was optimized on the average computed tomography (CT) to obtain optimal intensity of the carbon ions. From the optimized plan, dose distributions on individual phases of 4D-CT and 4D-CBCT were calculated by the Monte Carlo-based dose engine. Dose accumulation was performed on 4D-CBCT images using deformable vector fields (DVF) generated by SMEIR. The accumulated planning target volume (PTV) dose based on 4D-CBCT was then compared to the accumulated dose calculated on 4D-CT, where the DVFs between different phases were obtained by the demons deformable registration algorithm.
Dose value histograms (DVH) as well as absolute deviations of the maximum dose ( ), mean dose ( ), and dose coverage metrics ( and ) for PTV were quantitatively evaluated for the two sets of plans. Good agreement was found between the 4D-CT and 4D-CBCT-based PTV-DVH curves. The average values of , , and calculated between the 4D-CT and SMEIR-4D-CBCT-based plans were , , 2.12%, and , respectively, for the PTVs of ten patient case studies.
Based on these results, SMEIR-reconstructed 4D-CBCTs can potentially be used for motion estimation, dose evaluation, and adaptive treatment planning in lung cancer carbon ion therapy.
对于肺部肿瘤等移动靶区的碳离子治疗，运动管理至关重要。我们评估了使用 Simultaneous Motion Estimation and Image Reconstruction（SMEIR）重建的四维锥形束 CT（4D-CBCT）进行肺癌碳离子治疗中的剂量计算和积累的可行性。
使用 SMEIR 算法重建运动补偿的 4D-CBCT 图像，以在治疗日使用更新的相间运动模型捕获最新的解剖结构和运动。通过射线追踪技术从计划 4D-CT 模拟所有 CBCT 相位的投影。使用基于 GPU 的蒙特卡罗碳离子治疗剂量计算软件进行治疗计划和剂量计算。通过优化平均 CT 获得碳离子最佳强度，优化治疗计划。从优化计划中，通过基于蒙特卡罗的剂量引擎计算 4D-CT 和 4D-CBCT 各相位的剂量分布。使用由 SMEIR 生成的变形矢量场（DVF）在 4D-CBCT 图像上进行剂量积累。然后将基于 4D-CBCT 的累积计划靶区（PTV）剂量与基于 4D-CT 计算的累积剂量进行比较，其中通过 demons 变形配准算法获得不同相位之间的 DVFs。
对两组计划的 PTV 剂量值直方图（DVH）以及最大剂量（Dmax）、平均剂量（Dmean）和剂量覆盖指标（D95%和 D2%）的绝对偏差进行了定量评估。在 4D-CT 和基于 4D-CBCT 的 PTV-DVH 曲线之间发现了很好的一致性。在基于 SMEIR-4D-CBCT 的计划中，10 例患者研究的 PTV 的 、 、 计算的平均值分别为 、 、2.12%和 、 。
基于这些结果，SMEIR 重建的 4D-CBCT 可用于肺癌碳离子治疗中的运动估计、剂量评估和自适应治疗计划。
