Denis J M, Meulders J P, Lannoye E, Longrée Y, Ryckewaert G, Richard F, Vynckier S, Wambersie A
Service de Radiothérapie, Cliniques Universitaires St-Luc, Brussels, Belgium.
Bull Cancer Radiother. 1996;83 Suppl:160s-9s. doi: 10.1016/0924-4212(96)84904-8.
The multileaf collimator of the fast neutron therapy facility at Louvain-la-Neuve is described, as well as some of the physics experiments performed in order to evaluate the attenuation of neutron beams in different materials and thus optimize the composition of the collimator leaves. The multileaf collimator consists of two sets of 22 leaves each, which can be moved independently. They are made of iron and their thickness is 95 cm. Seven borated polyethylene disks are located in the distal part of the leaves in order to absorb more efficiently the low-energy component of the neutron spectrum. The width of the leaves is 1 cm at their distal part. The leaves can move 11 cm outwards and 6 cm inwards from their reference position, and field sizes up to 25.7 x 24.8 cm, as well as irregular field shapes, can be obtained. The inner part of the leaves and their two sides are always focused on the target. The complete multileaf collimator can rotate around the beam axis, from -90 degrees to +90 degrees from the reference position. The width of the penumbra (80-20% isodoses) is 0.64 cm and 1.17 cm at the depth of the maximum buildup and at 10 cm in depth respectively, for a 10 x 10 cm field size. The collimator is adequate for the energy of the p(65)+Be neutron beam of Louvain-la-Neuve and has been adapted to the fixed vertical beam. It has been designed following the original plans of Scanditronix, adjusted and fully assembled at the workshop of the Centre de Recherches du Cyclotron (CRC). Systematic measurements were performed in order to optimize the design and the composition of the leaves. In particular the attenuations of the actual beam and of monoenergetic neutron beams were measured in different materials such as iron and polyethylene. Above (upstream) the multileaf collimator, a fixed pre-collimator (iron thickness 50 cm; section 1 x 1 m) defines a conical aperture aligned on the largest opening of the leaves. It contains the two transmission chambers and a 2 cm thick polyethylene layer used for hardening the beam.
介绍了鲁汶新镇快中子治疗设施的多叶准直器，以及为评估中子束在不同材料中的衰减从而优化准直器叶片组成而进行的一些物理实验。多叶准直器由两组各22片叶片组成，它们可独立移动。叶片由铁制成，厚度为95厘米。七块含硼聚乙烯圆盘位于叶片的远端部分，以便更有效地吸收中子能谱的低能成分。叶片远端部分的宽度为1厘米。叶片可从其参考位置向外移动11厘米，向内移动6厘米，可获得最大尺寸为25.7×24.8厘米的射野以及不规则射野形状。叶片的内部及其两侧始终聚焦于靶区。整个多叶准直器可绕束轴旋转，相对于参考位置从 -90度到 +90度。对于10×10厘米的射野尺寸，在最大剂量建成深度处和10厘米深度处，半值层（80 - 20%等剂量线）的宽度分别为0.64厘米和1.17厘米。该准直器适用于鲁汶新镇p(65)+Be中子束的能量，并已适配固定的垂直束。它是按照Scanditronix的原始计划设计的，在回旋加速器研究中心（CRC）的车间进行了调整和完全组装。为了优化叶片的设计和组成进行了系统测量。特别是在铁和聚乙烯等不同材料中测量了实际束流和单能中子束的衰减。在多叶准直器上方（上游），一个固定的预准直器（铁厚度50厘米；截面1×1米）定义了一个与叶片最大开口对齐的锥形孔径。它包含两个传输室和一层用于束流硬化的2厘米厚聚乙烯层。
