Schätti A, Zakova M, Meer D, Lomax A J
Centre for Proton Therapy, Paul Scherrer Institut, Villigen, Switzerland.
Phys Med Biol. 2014 Jul 21;59(14):3813-28. doi: 10.1088/0031-9155/59/14/3813. Epub 2014 Jun 23.
Organ motion is one of the major obstacles in radiotherapy and charged particle therapy. Even more so, the theoretical advantages of dose distributions in scanned ion beam therapy may be lost due to the interplay between organ motion and beam scanning. Several techniques for dealing with this problem have been devised. In re-scanning, the target volume is scanned several times to average out the motion effects. In gating and breath-hold, dose is only delivered if the tumour is in a narrow window of position. Experiments have been performed to verify if gating and re-scanning are effective means of motion mitigation. Dose distributions were acquired in a lateral plane of a homogeneous phantom. For a spherical target volume and regular motion gating was sufficient. However, for realistic, irregular motion or a patient target volume, gating did not reduce the interplay effect to an acceptable level. Combining gating with re-scanning recovered the dose distributions. The simplest re-scanning approach, where a treatment plan is duplicated several times and applied in sequence, was not efficient. Simulations of different combinations of gating window sizes and re-scanning schemes revealed that reducing the gating window is the most efficient approach. However, very small gating windows are not robust for irregular motion.
器官运动是放射治疗和带电粒子治疗中的主要障碍之一。更甚的是，由于器官运动与束流扫描之间的相互作用，扫描离子束治疗中剂量分布的理论优势可能会丧失。已经设计了几种处理这个问题的技术。在重新扫描中，对靶体积进行多次扫描以平均运动效应。在门控和屏气技术中，只有当肿瘤处于狭窄的位置窗口时才给予剂量。已经进行了实验来验证门控和重新扫描是否是减轻运动的有效手段。在均匀体模的侧平面获取剂量分布。对于球形靶体积和规则运动，门控就足够了。然而，对于实际的不规则运动或患者靶体积，门控并没有将相互作用效应降低到可接受的水平。将门控与重新扫描相结合可恢复剂量分布。最简单的重新扫描方法，即多次复制治疗计划并依次应用，效率不高。对门控窗口大小和重新扫描方案的不同组合进行模拟表明，减小门控窗口是最有效的方法。然而，非常小的门控窗口对于不规则运动并不稳健。
