Meyer Jürgen, Richter Anne, Pfreundner Leo, Guckenberger Matthias, Krieger Thomas, Schwab Franz, Flentje Michael
Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand.
Med Dosim. 2009 Summer;34(2):170-8. doi: 10.1016/j.meddos.2008.11.004. Epub 2008 Dec 26.
Treatment of large target volumes with intensity modulated radiotherapy (IMRT) can be restricted by the maximum field size of the multileaf collimator (MLC). In this work, a straightforward technique for MLC-based IMRT is presented, which is generally applicable and does not depend on the capabilities of the linear accelerator's IMRT delivery system. A dual isocenter technique was developed that maximizes beam overlap. The beams at the first isocenter are arranged such that they interlace with the beams at the second isocenter. All beams contribute to the overlap region, whereas only some contribute to the superior and some to the inferior part of the target. The interlaced technique (9 beams) was compared with an alternative more complex approach (14 beams) for a head-and-neck case with simultaneous integrated boost and 3 different dose levels. The plans were compared in terms of complexity, dosimetry, and the effect of inaccurate translation between the isocenters. The interlaced and the more complex IMRT technique resulted in nearly identical dose distributions without clinically relevant differences. The total number of monitor units (MUs) was comparable with more MUs per segment for the interlaced technique. For the interlaced technique, the number of segments <or=5 MU was reduced by 43%. Simulation of isocenter setup errors of +/-1, +/-2, and +/-3 mm revealed maximum dose point errors of 1.8%, 3.8%, and 5.4% in the target volume for the interlaced technique. The interlaced IMRT technique resulted in an equivalent plan to the more complex technique without compromising the dose distribution. The technique is less complex and is robust against inaccurate isocenter translations of up to +/-1 mm. Due to the versatility of the technique, it can easily be applied to other anatomical regions and is well suited for clinical routine usage.
使用调强放疗（IMRT）治疗大靶区可能会受到多叶准直器（MLC）最大射野尺寸的限制。在这项工作中，提出了一种基于MLC的IMRT的直接技术，该技术普遍适用且不依赖于直线加速器IMRT输送系统的功能。开发了一种双等中心技术，可使射束重叠最大化。第一个等中心处的射束排列成与第二个等中心处的射束交错。所有射束都对重叠区域有贡献，而只有一些射束对靶区的上部有贡献，一些对下部有贡献。对于一个同时进行整合加量和三种不同剂量水平的头颈病例，将交错技术（9束射野）与另一种更复杂的方法（14束射野）进行了比较。从复杂性、剂量学以及等中心之间不准确平移的影响方面对计划进行了比较。交错技术和更复杂的IMRT技术产生了几乎相同的剂量分布，没有临床相关差异。总监测单位（MU）数量相当，交错技术每个射野的MU更多。对于交错技术，小于或等于5 MU的射野段数量减少了43%。模拟等中心设置误差为±1、±2和±3 mm时发现，交错技术在靶区内的最大剂量点误差分别为1.8%、3.8%和5.4%。交错IMRT技术产生的计划与更复杂的技术等效，且不影响剂量分布。该技术不太复杂，并且对于高达±1 mm的不准确等中心平移具有鲁棒性。由于该技术的通用性，它可以很容易地应用于其他解剖区域，非常适合临床常规使用。
