Neicu Toni, Shirato Hiroki, Seppenwoolde Yvette, Jiang Steve B
Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Phys Med Biol. 2003 Mar 7;48(5):587-98. doi: 10.1088/0031-9155/48/5/303.
Synchronized moving aperture radiation therapy (SMART) is a new technique for treating mobile tumours under development at Massachusetts General Hospital (MGH). The basic idea of SMART is to synchronize the moving radiation beam aperture formed by a dynamic multileaf collimator (DMLC) with the tumour motion induced by respiration. SMART is based on the concept of the average tumour trajectory (ATT) exhibited by a tumour during respiration. During the treatment simulation stage, tumour motion is measured and the ATT is derived. Then, the original IMRT MLC leaf sequence is modified using the ATT to compensate for tumour motion. During treatment, the tumour motion is monitored. The treatment starts when leaf motion and tumour motion are synchronized at a specific breathing phase. The treatment will halt when the tumour drifts away from the ATT and will resume when the synchronization between tumour motion and radiation beam is re-established. In this paper, we present a method to derive the ATT from measured tumour trajectory data. We also investigate the validity of the ATT concept for lung tumours during normal breathing. The lung tumour trajectory data were acquired during actual radiotherapy sessions using a real-time tumour-tracking system. SMART treatment is simulated by assuming that the radiation beam follows the derived ATT and the tumour follows the measured trajectory. In simulation, the treatment starts at exhale phase. The duty cycle of SMART delivery was calculated for various treatment times and gating thresholds, as well as for various exhale phases where the treatment begins. The simulation results show that in the case of free breathing, for 4 out of 11 lung datasets with tumour motion greater than 1 cm from peak to peak, the error in tumour tracking can be controlled to within a couple of millimetres while maintaining a reasonable delivery efficiency. That is to say, without any breath coaching/control, the ATT is a valid concept for some lung tumours. However, to make SMART an efficient technique in general, it is found that breath coaching techniques are required.
同步移动孔径放射治疗（SMART）是麻省总医院（MGH）正在研发的一种治疗移动肿瘤的新技术。SMART的基本理念是使由动态多叶准直器（DMLC）形成的移动辐射束孔径与呼吸引起的肿瘤运动同步。SMART基于肿瘤在呼吸过程中呈现的平均肿瘤轨迹（ATT）概念。在治疗模拟阶段，测量肿瘤运动并得出ATT。然后，使用ATT修改原始的调强放疗（IMRT）多叶准直器叶片序列，以补偿肿瘤运动。在治疗过程中，监测肿瘤运动。当叶片运动和肿瘤运动在特定呼吸阶段同步时开始治疗。当肿瘤偏离ATT时治疗将暂停，当肿瘤运动与辐射束之间重新建立同步时将恢复治疗。在本文中，我们提出了一种从测量的肿瘤轨迹数据中得出ATT的方法。我们还研究了正常呼吸期间ATT概念对肺部肿瘤的有效性。肺部肿瘤轨迹数据是在实际放疗期间使用实时肿瘤跟踪系统获取的。通过假设辐射束遵循得出的ATT且肿瘤遵循测量轨迹来模拟SMART治疗。在模拟中，治疗在呼气阶段开始。针对各种治疗时间、门控阈值以及治疗开始的各种呼气阶段，计算了SMART输送的工作周期。模拟结果表明，在自由呼吸的情况下，对于11个肺部数据集中肿瘤运动峰峰值大于1厘米的4个数据集，在保持合理输送效率的同时，肿瘤跟踪误差可控制在几毫米以内。也就是说，在没有任何呼吸指导/控制的情况下，ATT对于某些肺部肿瘤是一个有效的概念。然而，为了使SMART总体上成为一种高效技术，发现需要呼吸指导技术。
