The dosimetric parameters have an impact on the dose distribution especially in small fields defined by MLC. Therefore, it is necessary to perform different dosimetric verification of different collimators before any clinical implementation. Commercially, there are different collimator/MLC designs are available from various linac vendors. If the Radiotherapy department have more than one LINAC, the physicist should know the difference in the dose distribution with different LINAC head or with different MLCs even though it cannot be matched dosimetrically Many studies investigated dosimetric parameters by