[Multi-institutional Analysis of MLC Parameters for Commissioning of IMRT]

Multi-leaf collimator (MLC) parameters, which are registered with radiation treatment planning systems, are very important for intensity modulated radiation therapy (IMRT). In this study, we investigated MLC parameters of respective institutions for efficient commissioning of IMRT. Data of linac models, MLC types, nominal energy, irradiation technique, calculation algorithm, dosimetric leaf gap (DLG) values, and MLC transmission values were collected from each institution in which Varian linac and Eclipse were owned, and analyzed. The numbers of responses from institutions to questionnaire were 15, and the total number of linac was 22. In most institutions, volumetric modulated arc therapy (VMAT) technique was used, and the most used nominal energy was 10 MV. The higher nominal energy was, the higher values of MLC parameters (DLG and MLC transmission) were. In addition, values of MLC parameters of flattening filter free (FFF) beams were smaller than those of flattening filter (FF) beams, even when nominal energy was same. Values of DLG of VMAT tended to be greater than those of multi-field IMRT. These results are expected to be useful for institutions, in which IMRT is implemented.