This study was performed to verify scattered dose by collimator and block. As the results, the following conclusion have been reached ; 1. Scattered dose outside the treatment field increased with the increase of energy. 2. Shielding block cause 2 to 3 % Increase in central axis dose. 3. Scattered dose by the upper collimator was more than dose by the lower collimator. 4. It was found that optimal thickness of shielding block was 2 cm width.