Corvò R, Foppiano F, Orsatti M, Bisi F, Ghiso G, Martinelli R, Valanzola L, Vitale V
Servizio di Oncologia Radioterapica, Istituto Nazionale per la Ricerca sul Cancro di Genova.
Radiol Med. 1997 Nov;94(5):512-9.
The multileaf collimator (MLC) now commercially available as an integral or optional retrofit component of linear accelerator heads, permitting to shield automatically irregular fields by computerized movements of multiple tungsten leaves. In the present paper we discuss the main characteristics of different MLC versions, MLC dosimetric drawbacks and the clinical fields where the MLC could he widely used.
Since February, 1995, we have studied the dosimetric characteristics and clinical implications of a multileaf collimator of a Clinac 2100 C/D linear accelerator used to replace conventional low melting alloy blocks. The scalloping effect of isodoses and the effective penumbra produced by the multileaf collimator in an irregular field were analyzed accurately. Secondly, radiation leakage through tungsten leaves was measured and compared with the values of low melting alloy blocks. Finally, the MLC was extensively used in clinical practice for the radiotherapy of different tumors.
Different dosimetric steps were followed to obtain the monitor units/dose ratio. Our single MLC-shielded irregular fields measurements also showed several physical and dosimetric disadvantages related to wider effective penumbra than with conventional shielding when the angle between field margin and the normal to the direction of leaf travel is 45 degrees. In clinical practice, the MLC can be widely used for the conformal radiotherapy of pelvic and thoracic tumors. Conventional low melting alloy blocks should be replaced with MLC for radiotherapy of selected brain and head and neck cancers.
The current use of a multileaf collimator improves both the accuracy and the effectiveness of radiation therapy and reduces the time for every treatment dose, which potentially increases the number of patients treated every day. The multileaf collimator is presently an important technical tool either to replace conventional shielding for static conformational radiotherapy or to administer 3D-planned dynamic radiotherapy.
多叶准直器（MLC）目前作为直线加速器机头的一个整体或可选的改装部件在市场上销售，它通过多个钨叶的计算机控制运动来自动屏蔽不规则射野。在本文中，我们讨论了不同版本MLC的主要特性、MLC的剂量学缺点以及MLC可广泛应用的临床领域。
自1995年2月以来，我们研究了用于替代传统低熔点合金挡块的Clinac 2100 C/D直线加速器的多叶准直器的剂量学特性和临床意义。精确分析了不规则射野中多叶准直器产生的等剂量曲线的扇贝效应和有效半值层。其次，测量了通过钨叶的辐射泄漏，并与低熔点合金挡块的值进行了比较。最后，MLC在不同肿瘤的放射治疗临床实践中得到了广泛应用。
采用不同的剂量学步骤来获得监测单位/剂量比。我们对单个MLC屏蔽的不规则射野的测量还显示，当射野边缘与叶片行进方向的法线之间的夹角为45度时，与传统屏蔽相比，有效半值层更宽，存在一些物理和剂量学上的缺点。在临床实践中，MLC可广泛用于盆腔和胸部肿瘤的适形放疗。对于某些脑癌以及头颈部癌的放疗，应使用MLC替代传统的低熔点合金挡块。
目前多叶准直器的使用提高了放射治疗的准确性和有效性，并减少了每次治疗剂量的时间，这有可能增加每天治疗的患者数量。多叶准直器目前是一种重要的技术工具，既可以替代传统屏蔽用于静态适形放疗，也可以用于实施三维计划的动态放疗。
