Karlsson M, Zackrisson B
Department of Radiation Physics, University of Umeå, Sweden.
Radiother Oncol. 1993 Dec;29(3):317-26. doi: 10.1016/0167-8140(93)90150-7.
Multi-leaf collimators (MLCs) are offered as an accessory to many accelerators for radiation therapy. However, beam edges generated with these collimators are not as smooth as can be achieved with individually made blocks. The clinical drawbacks and benefits of this ripple were evaluated both for single field treatments and for combined adjacent fields of different beam qualities. In this investigation the MLC-collimated beams of the MM50 racetrack microtron were studied. The distance between the field edge and the 90% isodose was measured at the reference depth for four beam qualities (20 MV photons and 10, 20 and 50 MeV electrons). This distance was found to vary from approximately 6 mm for straight beam edges (i.e., all collimator leaves aligned) to approximately 2 mm from the tip of the leaves for a saw-tooth shaped beam edge. The over- and under-dosage in the joint between combined adjacent fields was found to be typically +/- 10% in small volumes. Improved clinical techniques using adjacent photon and electron fields with the same isocentre and source position (without moving the gantry) have been developed. For treatments of the breast, including the mammary chain, a uniform dose distribution was created with special attention given to the irradiation of the heart and lung outside the target volume. A method for head and neck treatments was optimised to give uniform dose distribution in the joint between the photon and electron fields and a method of treating the mediastinum, including the chest wall in front of the left lung, was analysed with respect to dose uniformity in the tumour and shielding of the lung.
多叶准直器（MLC）作为许多放射治疗加速器的附件提供。然而，使用这些准直器产生的射束边缘不如单独制作的挡块所达到的那样平滑。针对单野治疗以及不同射束质量的相邻野组合，评估了这种波纹的临床缺点和优点。在本研究中，对MM50跑道式电子回旋加速器的MLC准直射束进行了研究。在参考深度处，针对四种射束质量（20 MV光子以及10、20和50 MeV电子）测量了射野边缘与90%等剂量线之间的距离。发现该距离从直边射野（即所有准直器叶片对齐）时的约6 mm变化到锯齿形射野边缘时距叶片尖端约2 mm。发现相邻野组合处小体积内的剂量过量和不足通常为±10%。已经开发出使用具有相同等中心和源位置（不移动机架）的相邻光子和电子野的改进临床技术。对于包括乳腺链在内的乳腺治疗，创建了均匀的剂量分布，并特别关注靶体积外心脏和肺部的照射。优化了一种用于头颈部治疗的方法，以在光子和电子野之间的接合处提供均匀的剂量分布，并分析了一种治疗纵隔（包括左肺前方胸壁）的方法在肿瘤中的剂量均匀性和肺部屏蔽情况。
