Quality Control For Two Types Of Radiotherapy Multileaf Collimators
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The purpose of our study was to describe the performance characteristics of two MLC systems (Elekta and Siemens) having different leaf width respectively to improve the available data. Furthermore, the work suggests an adequate QA program to be performed during routine treatment delivery.
Methods and Material: The Leaf leakage, tongueand- groove effect, identification between lightfield and radiation field , measurement of penumbra for all borders of MLC leaves, Penumbra measurements in the direction of leaf motion, Penumbra measurements for stepped MLC edges, Precise position of MLCs of a highenergy photon (6 MV) Elekta and Siemens linear accelerator were measured using Kodak X-Omat V film.
Results : The results of leaf transmission agree with literature data dealing with the same MLC. The value obtained of the dose reduction for the tongue-and-groove effect is greater than other reports .Measurements of identification between light field and radiation field showed that, the difference between them ranged from 2 mm to 3mm. The penumbra width is independent of leaf position. For stepped edge, the measured penumbra width for MLC is larger than custom blocks about 2mm for erect edge and 2 mm for 45o angled edge, there is small difference in position accuracy of leaves due to the effect of gravity.
Conclusions: The results showed that, it is important to know the dosimetric characteristicsof MLC to know its effect in the treatment process.
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