Bayouth J E, Morrill S M
University of Texas Medical Branch, Department of Radiation Oncology, Galveston, Texas 77555, USA.
Med Phys. 2003 Sep;30(9):2545-52. doi: 10.1118/1.1603743.
The objective of this work was to measure the performance characteristics of a double-focus multileaf collimator (MLC) for intensity modulated radiation therapy (IMRT), specifically the variation in penumbra and leakage for narrow fields as a function of field position over a 20x27 cm space available for segmented MLC IMRT. Measurements were made with 6 MV x rays through a MLC containing 29 leaf pairs (27 pairs of 1 cm width), and EDR2 film at 10 cm depth in solid water at 100 cm SAD. Films were digitized with 0.17 mm resolution and converted to dose. Interleaf and intraleaf transmission were measured along 11 vertical profile locations. Leaf-end transmission was measured along horizontal profiles for each of 9 different leaf abutments, traveling over a 20 cm range. In-plane penumbra measurements were made through a single leaf retracted, for 7 different leaves. Cross-plane penumbra (leaf-end) measurements were made for all 27 leaf pairs, where the 1 cm field width was placed in 11 different off-axis positions (20 cm range). Interleaf leakage (range 1.0%-1.5%), intraleaf transmission (range 0.6%-0.8%), and leaf-end transmission (range 0.8%-2.7%) were consistent for all leaf pairs at a given abutment position. The penumbra for these 1-cm-wide fields was measured to be 0.36 cm+/-0.03 cm for 99% of the measurements. In conclusion, the penumbra and leakage of the double-focus MLC were remarkably consistent for the range of leaf positions studied, producing dosimetric characteristics that are well suited for IMRT segments where opposing leaf pairs are often separated by 10 mm or less.
这项工作的目的是测量用于调强放射治疗（IMRT）的双聚焦多叶准直器（MLC）的性能特征，具体而言，是测量在20×27 cm空间内，用于分段MLC IMRT的窄射野的半值层和泄漏随射野位置的变化，该空间可供使用。测量使用6 MV X射线，通过一个包含29对叶片（27对1 cm宽的叶片）的MLC进行，在100 cm源轴距下，于固体水模体中10 cm深度处使用EDR2胶片。胶片以0.17 mm的分辨率进行数字化处理并转换为剂量。沿11个垂直剖面位置测量叶片间和叶片内的透射率。对于9种不同的叶片对接情况，在20 cm范围内沿水平剖面测量叶片末端透射率。对于7片不同的叶片，通过单个叶片缩回测量平面内半值层。对所有27对叶片进行跨平面半值层（叶片末端）测量，其中1 cm的射野宽度放置在11个不同的离轴位置（20 cm范围）。在给定的对接位置，所有叶片对的叶片间泄漏（范围为1.0% - 1.5%）、叶片内透射率（范围为0.6% - 0.8%）和叶片末端透射率（范围为0.8% - 2.7%）是一致的。对于这些1 cm宽的射野，99%的测量中半值层测量值为0.36 cm±0.03 cm。总之，在所研究的叶片位置范围内，双聚焦MLC的半值层和泄漏非常一致，产生的剂量学特征非常适合于IMRT分段，在这种情况下，相对的叶片对通常相隔10 mm或更小。
