Department of Physics, Karunya Institute of Technology and Sciences, Coimbatore, India.
Department of Oncology, Aster Malabar Institute of Medical Sciences, Calicut, India.
Asian Pac J Cancer Prev. 2021 Dec 1;22(12):3883-3888. doi: 10.31557/APJCP.2021.22.12.3883.
The present study aims to compare different dosimetric parameters from field sizes defined by secondary and tertiary collimators. A comparison has been drawn between two types of Multi Leaf Collimator (MLC) designs.
The measurements were obtained using Millennium MLC (Mi-MLC) from Varian Unique™ linear accelerator (LINAC-1) and compared with measurements from Varian Truebeam™ linear accelerator (LINAC-2) using High Definition MLC (HD-MLC). Dosimetric analysis included percentage depth dose (PDD), cross profile, dosimetric leaf gap (DLG) and scatter factor (SF) that were taken for different field sizes defined by both the MLC design and jaw. For beam data measurement PTW Radiation field analyse (RFA) was utilized.
When the surface dose for MLC field for linac 1 and linac 2 were compared with jaws they were found to be on the higher side that is 2.8% to 4.9% and 2.2% to 3.6% respectively. The SF was found to vary from -3.2% to 0.73% for LINAC-1 with Mi-MLC when compared with jaws. Similarly, the SF variation from -2.4% to 1.1% was observed for LINAC-2 with HD-MLC as compared with jaw. Larger field sizes gave increased SF while smaller field sizes showed the opposite for HD-MLC. The penumbra was found to be less in HD-MLC as compared to Mi-MLC. Similarly, DLG was found to reduce by 0.056 mm in Mi-MLC when compared with HD-MLC. The results of symmetry and flatness were seen within the limits for both MLC designs.
It can be concluded from the results that both the MLC designs have merits and demerits that are based on their effectiveness and clinical use. However, higher surface dose was found in HD-MLC in contrast to Mi-MLC.
本研究旨在比较由次级和 tertiary 准直器定义的射野大小的不同剂量学参数。比较了两种多叶准直器（MLC）设计。
使用瓦里安独特直线加速器（LINAC-1）的 Millennium MLC（Mi-MLC）进行测量，并与瓦里安 Truebeam 直线加速器（LINAC-2）使用高清晰度 MLC（HD-MLC）进行的测量进行比较。剂量学分析包括百分深度剂量（PDD）、十字形剖面、剂量学叶片间隙（DLG）和散射因子（SF），这些参数是针对由 MLC 设计和准直器定义的不同射野大小而获得的。对于光束数据测量，使用了 PTW 辐射场分析（RFA）。
当比较 LINAC-1 和 LINAC-2 的 MLC 射野的表面剂量与准直器时，发现它们的剂量高于准直器，分别为 2.8%至 4.9%和 2.2%至 3.6%。当与准直器相比时，发现 LINAC-1 与 Mi-MLC 的 SF 变化范围为-3.2%至 0.73%。同样，对于 LINAC-2 与 HD-MLC，与准直器相比，SF 的变化范围为-2.4%至 1.1%。较大的射野大小会增加 SF，而较小的射野大小则相反，对于 HD-MLC 则如此。与 Mi-MLC 相比，发现 HD-MLC 的半影更小。同样，与 HD-MLC 相比，Mi-MLC 的 DLG 减少了 0.056 毫米。两种 MLC 设计的对称性和平坦度结果均在限制范围内。
从结果可以得出结论，两种 MLC 设计都有其优点和缺点，这取决于它们的有效性和临床应用。然而，与 Mi-MLC 相比，HD-MLC 的表面剂量更高。
