Williams M J, Metcalfe P
Department of Medical Physics, Illawarra Cancer Care Centre, Crown St, Wollongong, NSW 2500, Australia.
Phys Med Biol. 2006 Feb 21;51(4):N65-78. doi: 10.1088/0031-9155/51/4/N03. Epub 2006 Feb 1.
A new multileaf collimator (MLC) model has been incorporated into version 7.4 of the Pinnacle radiotherapy treatment planning system (Philips Radiation Oncology Systems, Milpitas, CA). The MLC model allows for rounded MLC leaf-ends and provides separate parameters for inter-leaf transmission, intra-leaf transmission and the tongue width of the MLC leaf. In this report we detail the method followed to commission the MLC model for a Varian 120-leaf Millennium MLC (Varian Medical Systems, Palo Alto, CA, USA) for both 6 and 10 MV photons, and test the validity of the model for an IMRT field. Dose profiles in water were measured for a range of square MLC field sizes and compared to the Pinnacle computed dose profiles; in addition, the dose distribution for a series of adjacent MLC fields was measured to observe the model's behaviour along match-lines. Based on these results intra-leaf transmissions of 1.5% for 6 MV and 1.8% for 10 MV, leaf-tip radius of 12.0 cm, an inter-leaf transmission of 0.5%, and a tongue width of 0.1 cm were chosen. Using these values to compute the planar dose distribution for a 6 MV IMRT field, the new version of Pinnacle displayed improved dosimetric agreement with the dose-to-water EPID image and ion chamber measurements when compared to the old version of Pinnacle, particularly along the MLC tongue edge and across match-lines. Discrepancies of up to 5% were observed between calculated and measured doses along match-lines for both 6 MV and 10 MV photons; however, the new MLC model did predict the presence of match-lines and was a significant improvement on the previous model.
一种新的多叶准直器（MLC）模型已被纳入Pinnacle放射治疗计划系统7.4版本（飞利浦放射肿瘤系统公司，加利福尼亚州米尔皮塔斯）。该MLC模型允许MLC叶片末端呈圆形，并为叶片间透射、叶片内透射和MLC叶片的舌形宽度提供单独的参数。在本报告中，我们详细介绍了针对瓦里安120叶Millennium MLC（美国加利福尼亚州帕洛阿尔托市瓦里安医疗系统公司）的6和10 MV光子调试MLC模型所遵循的方法，并测试该模型在调强放疗（IMRT）射野中的有效性。测量了一系列方形MLC射野尺寸在水中的剂量分布，并与Pinnacle计算的剂量分布进行比较；此外，还测量了一系列相邻MLC射野的剂量分布，以观察该模型在匹配线上的表现。基于这些结果，选择了6 MV时叶片内透射率为1.5%、10 MV时为1.8%，叶片尖端半径为12.0 cm，叶片间透射率为0.5%，以及舌形宽度为0.1 cm。使用这些值计算6 MV IMRT射野的平面剂量分布，与旧版本的Pinnacle相比，新版本的Pinnacle在剂量学上与水模剂量EPID图像和电离室测量结果的一致性得到了改善，特别是在MLC舌形边缘和匹配线上。对于6 MV和10 MV光子，在匹配线上计算剂量和测量剂量之间观察到高达5%的差异；然而，新的MLC模型确实预测了匹配线的存在，并且比先前的模型有显著改进。
