Tsunashima Yoshikazu, Vedam Sastry, Dong Lei, Umezawa Masumi, Sakae Takeji, Bues Martin, Balter Peter, Smith Alfred, Mohan Radhe
Department of Radiation Physics, The University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd., Unit 94, Houston, TX 77030, USA.
Phys Med Biol. 2008 Apr 7;53(7):1947-59. doi: 10.1088/0031-9155/53/7/010. Epub 2008 Mar 11.
Significant differences exist in respiratory-gated proton beam delivery with a synchrotron-based accelerator system when compared to photon therapy with a conventional linear accelerator. Delivery of protons with a synchrotron accelerator is governed by a magnet excitation cycle pattern. Optimal synchronization of the magnet excitation cycle pattern with the respiratory motion pattern is critical to the efficiency of respiratory-gated proton delivery. There has been little systematic analysis to optimize the accelerator's operational parameters to improve gated treatment efficiency. The goal of this study was to estimate the overall efficiency of respiratory-gated synchrotron-based proton irradiation through realistic simulation. Using 62 respiratory motion traces from 38 patients, we simulated respiratory gating for duty cycles of 30%, 20% and 10% around peak exhalation for various fixed and variable magnet excitation patterns. In each case, the time required to deliver 100 monitor units in both non-gated and gated irradiation scenarios was determined. Based on results from this study, the minimum time required to deliver 100 MU was 1.1 min for non-gated irradiation. For respiratory-gated delivery at a 30% duty cycle around peak exhalation, corresponding average delivery times were typically three times longer with a fixed magnet excitation cycle pattern. However, when a variable excitation cycle was allowed in synchrony with the patient's respiratory cycle, the treatment time only doubled. Thus, respiratory-gated delivery of synchrotron-based pulsed proton irradiation is feasible and more efficient when a variable magnet excitation cycle pattern is used.
与使用传统直线加速器的光子治疗相比，基于同步加速器的加速器系统在呼吸门控质子束输送方面存在显著差异。同步加速器输送质子受磁体励磁循环模式的控制。磁体励磁循环模式与呼吸运动模式的最佳同步对于呼吸门控质子输送的效率至关重要。目前很少有系统分析来优化加速器的运行参数以提高门控治疗效率。本研究的目的是通过实际模拟估计基于同步加速器的呼吸门控质子照射的整体效率。我们使用来自38名患者的62条呼吸运动轨迹，针对各种固定和可变磁体励磁模式，在呼气峰值周围模拟了占空比为30%、20%和10%的呼吸门控。在每种情况下，确定了在非门控和门控照射场景下输送100个监测单位所需的时间。基于本研究的结果，非门控照射输送100 MU所需的最短时间为1.1分钟。对于在呼气峰值周围占空比为30%的呼吸门控输送，使用固定磁体励磁循环模式时，相应的平均输送时间通常要长三倍。然而，当允许可变励磁循环与患者的呼吸周期同步时，治疗时间仅增加一倍。因此，当使用可变磁体励磁循环模式时，基于同步加速器的脉冲质子照射的呼吸门控输送是可行且更有效的。
