Objective To explore the necessity and feasibility of the real-time treatment planning optimization by CT guided with ¹²⁵I seed implantation brachytherapy treatment to thoracic malignancies. Methods To retrospectively analyze the data of 31 inpatients (from October 2010 to June 2012) with thoracic malignancie by CT guidance ¹²⁵I brachytherapy. The real-time planning optimization were applicated to 13 cases (group A), 18 patients undergoing experience particles implantation interval 1 cm (group B), all the patients were prescribed dose 110 Gy and post-planning verified after surgery. Re-simulation of real-time program (group C) about the image data in group B, data analysis was χ²-test by SPSS 13.0 software. Results The quality verification in two groups were 92% and 39%,the difference was statistically sifnificant (P=0.003). The re-simulation program in group C was 94%,there was significant difference compared with group B (P=0.001),but with no significant difference compared with group A (P=0.811). Conclusions The application of intraoperative real-time planning by CT guided with ¹²⁵I seed implantation brachytherapy to thoracic malignancies, non-equidistant layout that be the real implantedneedle trajectory based on dosimetry, can significantly improve the tumor target dose, operational, there was greatly important value to the standardization of the particle therapy of thoracic malignancies.