Center for Proton Radiation Therapy, Paul Scherrer Institut, 5232 Villigen-PSI, Switzerland.
Phys Med Biol. 2010 Aug 21;55(16):4771-82. doi: 10.1088/0031-9155/55/16/010. Epub 2010 Aug 3.
Proton therapy can be particularly sensitive to changes or errors in range. Thus, methods for the in vivo measurement of range could be of great use to improve the quality and accuracy of proton-based radiotherapy. In this paper, we introduce the concept of the 'range probe'. This is a low-dose, high-energy proton pencil beam that would pass through a patient, and whose integral Bragg peak would be measured on the exit side using a multi-layer detector. We propose that by comparing the measured integral Bragg peak with that calculated based on the patient's planning CT, such a range probe could provide useful information about the accuracy of range calculations in vivo. To study the feasibility of this approach, a Monte Carlo-based study has been performed. Using a patient's planning CT, MC simulations (VMCpro) have been made for single pencil beams laterally traversing the head and stopping in a simulated range telescope behind the patient. Range probes have been calculated for different locations, and the residual range from the Bragg peak 'signal' in the range telescope has been assessed for different assumed detector thicknesses. The sensitivity of this approach to changes in CT values, calibration curve and positional shifts of the CT have been investigated. From our analysis, range resolutions of 1 mm may be possible with a detector thickness of 4 mm for homogeneous regions. Additionally, for heterogeneous regions, changes of the Bragg peak shape due to spatial shifts of the CT could be a sensitive measure for detecting patient set-up errors directly in the treatment position. The concept of the proton 'range probe' appears to be feasible for high-resolution range verification. We now want to test this concept experimentally using different possible range telescope detectors.
质子治疗对射程的变化或误差特别敏感。因此，用于体内测量射程的方法可能对提高质子放射治疗的质量和准确性有很大的帮助。在本文中，我们介绍了“射程探头”的概念。这是一种低剂量、高能质子铅笔束，它将穿过患者，其积分布拉格峰将在出口侧使用多层探测器进行测量。我们提出，通过比较测量的积分布拉格峰与基于患者计划 CT 的计算值，这种射程探头可以提供有关体内射程计算准确性的有用信息。为了研究这种方法的可行性，已经进行了基于蒙特卡罗的研究。使用患者的计划 CT，对横向穿过头部的单个铅笔束进行了 MC 模拟（VMCpro），并在患者后面的模拟射程望远镜中停止。为不同位置计算了射程探头，并评估了不同假设探测器厚度下在射程望远镜中的布拉格峰“信号”的剩余射程。研究了这种方法对 CT 值、校准曲线和 CT 位置偏移变化的灵敏度。从我们的分析来看，对于均匀区域，探测器厚度为 4 毫米时，可能达到 1 毫米的射程分辨率。此外，对于非均匀区域，由于 CT 的空间移位导致的布拉格峰形状的变化可能是直接在治疗位置检测患者设置误差的敏感指标。质子“射程探头”的概念似乎适用于高分辨率的射程验证。我们现在希望使用不同的可能的射程望远镜探测器来对此概念进行实验测试。
