RESUMO
Objective To study the influence of the angle of multileaf collimator leaves on segments (control point for sliding windows) number and monitor units in intensity-modulated radiotherapy (IMRT) plan optimization.Methods 10 cases undergone IMRT with rectangle target volume were choosed,2 plan were designed with step and shot technique and sliding windows technique for running direction of collimator with target long axis vertical and parallel respectively,compared the plans with similar optimization parameters for different angle of the collimator.Results The number of segments and monitor units increased by 52.8％ and 49.6％ more than longitudinal direction of leaf collimator with static IMRT respectively,there appeared significant difference (P =0.000) ; and the number of segments and monitor units increased by 58.2％ and 61.9％ more than longitudinal direction of leaf collimator with dynamic IMRT respectively,there appeared significant difference (P =0.000).Conclusions For the optimization of IMRT based on multileaf collimator,the direction of collimator perpendicular to the target long axis,there could be obviously decrease the number of monitor units,shorten the treatment time,improve the treatment efficiency with similar dose distribution.