Kontaxis C, Bol G H, Stemkens B, Glitzner M, Prins F M, Kerkmeijer L G W, Lagendijk J J W, Raaymakers B W
Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, The Netherlands.
Phys Med Biol. 2017 Aug 21;62(18):7233-7248. doi: 10.1088/1361-6560/aa82ae.
The hybrid MRI-radiotherapy machines, like the MR-linac (Elekta AB, Stockholm, Sweden) installed at the UMC Utrecht (Utrecht, The Netherlands), will be able to provide real-time patient imaging during treatment. In order to take advantage of the system's capabilities and enable online adaptive treatments, a new generation of software should be developed, ranging from motion estimation to treatment plan adaptation. In this work we present a proof of principle adaptive pipeline designed for high precision stereotactic body radiation therapy (SBRT) suitable for sites affected by respiratory motion, like renal cell carcinoma (RCC). We utilized our research MRL treatment planning system (MRLTP) to simulate a single fraction 25 Gy free-breathing SBRT treatment for RCC by performing inter-beam replanning for two patients and one volunteer. The simulated pipeline included a combination of (pre-beam) 4D-MRI and (online) 2D cine-MR acquisitions. The 4DMRI was used to generate the mid-position reference volume, while the cine-MRI, via an in-house motion model, provided three-dimensional (3D) deformable vector fields (DVFs) describing the anatomical changes during treatment. During the treatment fraction, at an inter-beam interval, the mid-position volume of the patient was updated and the delivered dose was accurately reconstructed on the underlying motion calculated by the model. Fast online replanning, targeting the latest anatomy and incorporating the previously delivered dose was then simulated with MRLTP. The adaptive treatment was compared to a conventional mid-position SBRT plan with a 3 mm planning target volume margin reconstructed on the same motion trace. We demonstrate that our system produced tighter dose distributions and thus spared the healthy tissue, while delivering more dose to the target. The pipeline was able to account for baseline variations/drifts that occurred during treatment ensuring target coverage at the end of the treatment fraction.
像安装在荷兰乌得勒支大学医学中心（UMC Utrecht，荷兰乌得勒支）的磁共振直线加速器（MR-linac，瑞典斯德哥尔摩的医科达公司）这样的混合式磁共振放疗设备，将能够在治疗期间提供实时患者成像。为了利用该系统的功能并实现在线自适应治疗，应该开发新一代软件，从运动估计到治疗计划调整。在这项工作中，我们展示了一种原理验证自适应流程，该流程专为高精度立体定向体部放射治疗（SBRT）设计，适用于受呼吸运动影响的部位，如肾细胞癌（RCC）。我们利用我们的研究型磁共振治疗计划系统（MRLTP），通过对两名患者和一名志愿者进行束间重新计划，模拟了针对RCC的单次分割25 Gy自由呼吸SBRT治疗。模拟流程包括（束前）4D-MRI和（在线）2D电影MRI采集的组合。4D-MRI用于生成中位参考体积，而电影MRI通过内部运动模型提供描述治疗期间解剖结构变化的三维（3D）可变形矢量场（DVF）。在治疗分割期间，在束间间隔时，更新患者的中位体积，并根据模型计算的基础运动精确重建已交付的剂量。然后使用MRLTP模拟快速在线重新计划，以最新解剖结构为目标并纳入先前交付的剂量。将自适应治疗与传统的中位SBRT计划进行比较，该计划在相同运动轨迹上重建了3毫米的计划靶体积边缘。我们证明，我们的系统产生了更紧密的剂量分布，从而保护了健康组织，同时向靶区输送了更多剂量。该流程能够考虑治疗期间发生的基线变化/漂移，确保在治疗分割结束时实现靶区覆盖。
