Eley John Gordon, Newhauser Wayne David, Richter Daniel, Lüchtenborg Robert, Saito Nami, Bert Christoph
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA. The University of Texas Graduate School of Biomedical Sciences at Houston, 6767 Bertner Avenue, Houston, TX 77030, USA. Department of Radiation Oncology, University of Maryland School of Medicine, 22 South Green Street, Baltimore, MD 21201, USA.
Phys Med Biol. 2015 Feb 21;60(4):1717-40. doi: 10.1088/0031-9155/60/4/1717. Epub 2015 Feb 4.
Beam tracking with scanned carbon ion radiotherapy achieves highly conformal target dose by steering carbon pencil beams to follow moving tumors using real-time magnetic deflection and range modulation. The purpose of this study was to evaluate the robustness of target dose coverage from beam tracking in light of positional uncertainties of moving targets and beams. To accomplish this, we simulated beam tracking for moving targets in both water phantoms and a sample of lung cancer patients using a research treatment planning system. We modeled various deviations from perfect tracking that could arise due to uncertainty in organ motion and limited precision of a scanned ion beam tracking system. We also investigated the effects of interfractional changes in organ motion on target dose coverage by simulating a complete course of treatment using serial (weekly) 4DCTs from six lung cancer patients. For perfect tracking of moving targets, we found that target dose coverage was high ([Formula: see text] was 94.8% for phantoms and 94.3% for lung cancer patients, respectively) but sensitive to changes in the phase of respiration at the start of treatment and to the respiratory period. Phase delays in tracking the moving targets led to large degradation of target dose coverage (up to 22% drop for a 15° delay). Sensitivity to technical uncertainties in beam tracking delivery was minimal for a lung cancer case. However, interfractional changes in anatomy and organ motion led to large decreases in target dose coverage (target coverage dropped approximately 8% due to anatomy and motion changes after 1 week). Our findings provide a better understand of the importance of each of these uncertainties for beam tracking with scanned carbon ion therapy and can be used to inform the design of future scanned ion beam tracking systems.
扫描碳离子放射治疗中的束流跟踪通过实时磁偏转和射程调制引导碳笔形束流跟踪移动肿瘤，从而实现高度适形的靶区剂量。本研究的目的是根据移动靶区和束流的位置不确定性，评估束流跟踪靶区剂量覆盖的稳健性。为实现这一目的，我们使用研究型治疗计划系统在水模体和肺癌患者样本中模拟了移动靶区的束流跟踪。我们对由于器官运动不确定性和扫描离子束跟踪系统精度有限可能出现的各种与完美跟踪的偏差进行了建模。我们还通过模拟六名肺癌患者的连续（每周）4DCT完整治疗疗程，研究了器官运动的分次间变化对靶区剂量覆盖的影响。对于移动靶区的完美跟踪，我们发现靶区剂量覆盖较高（水模体中[公式：见原文]分别为94.8%，肺癌患者中为94.3%），但对治疗开始时呼吸相位的变化和呼吸周期敏感。跟踪移动靶区的相位延迟会导致靶区剂量覆盖大幅下降（延迟15°时下降高达22%）。对于肺癌病例，对束流跟踪传输中技术不确定性的敏感性最小。然而，解剖结构和器官运动的分次间变化导致靶区剂量覆盖大幅下降（1周后由于解剖结构和运动变化，靶区覆盖下降约8%）。我们的研究结果有助于更好地理解这些不确定性中的每一个对于扫描碳离子治疗束流跟踪的重要性，并可用于为未来扫描离子束跟踪系统的设计提供参考。
