Introduction:
 




 Multileaf collimators (MLCs) are computer-controlled devices which are Useful and cost-effective tools for conformal therapy and intensity modulation radiotherapy (IMRT).
Nowadays MLCs are important and standard configuration of the new medical linear accelerators which are substitute of conventional Blocks and has eliminated the difficulties of working with blocks. MLCs are available from many manufacturers and their designs differ in the way they couple with conventional jaws, number and width of leaves and in their physical and dosimetric characteristics, well understanding on the mechanics and dosimetric characteristics of MLC is the basic task of medical physicist.




 
Materials and Methods:




 In this study some mechanical and dosimetric characteristics of a P.E. Collimators Add-On MLC which is installed on VARIAN CLINAC 2100 C/D are presented. Scatter factors (Sc, Sp, Scp), central axis depth dose and beam profiles were measured before and after installation of MLC. mechanical and Leaf Leakages for 6MV and 18MV beams were measured with Gafchromic EBT3 films.




 
Results:




 radiation and light fields were match below the 2mm acceptable level based on AAPM reports. Average leaf leakage was noted 1.79% for 6MV and 1.98% for 18MV beams, respectively. No significant differences were found in beam profiles, collimator (Sc), phantom (Sp) and total (Sc, p) scatter factors after MLC installation. The percent depth dose data for all fields and both beam energies were within 1.6 % of the original data.




 
 
Conclusion:




 Based on the Mechanical and dosimetric results which have been achieved from our different standard tests, we found no significant differences between before and after MLC installation Values on Clinac 2100 C/D Varian LINAC.