ABSTRACT
The objective was to perform a direct comparison of cerrobend blocks to "Best fit" single field Multileaf collimator [MLC] shapes. Output measurements were made on a primus Linear Accelerator [Siemens], 29 leaves per side for Photon beam energy 6MV at source-to- axis distance [SAD 100cm]. The data was measured for different field sizes at different depths. The field sizes dependent factors were measured at the maximum depth 1.6cm for this energy. The penumbra widths were measured at 10cm depth in solid phantom by using Kodak films, their values were 5-6mm for isodose lines [80%-20%] and 16- 17mm for isodose lines [90%-10%]. The average MLC factor [MLC reading divided by block reading] was found to be 1. Also the comparison between the isodose mapping was obtained by the Multidata system for shaping treatment field in Head and Neck Cancer with both MLC and Cerrobend blocks at clinical depth 5cm