Dosimetric optimization of 125I seed implantation and improvement of the therapeutic outcome for treating non-small cell lung cancer

Objective To implement a dose optimization programme and improve the therapeutic gain ratio of 125I seed implantation in patients with stage IIIb to IV NSCLC. Methods A total of 246 NSCLC patients (158 males, 88 females, mean age 61.7 years) were enrolled into this study. The target was located by CT, 18F-FDG coincidence SPECT/CT or flexible fiberoptic bronchoscopy (FFB). The treatment plan was generated and optimized by TPS, which was evaluated according to the dose volume histograms (DVH). 125I seeds were implanted and intraoperative position was validated in real time under guidance of imaging. Dosimetry was validated, and therapeutic efficiency was evaluated. The 1-and 2-year survival rates were calculated. Results The number and distribution of the implanted seeds were accorded with those planned by TPS in 129 of 137 cases (94.16%) in CT guided implantation group. The matched peripheral dose (MPD) was 92.1 Gy. The average dose of organs at risk such as heart, lung and spinal cord was significantly lower than the normal tissue tolerance dose. The early and late radioactive response rates were 12.41%(17/137) and 2.19%(3/137) respectively, and 91.97%(126/137) was under local control. The 1-and 2-year survival rates was 91.24 %(125/137) and 50.36 %(69/137) respectively. In SPECT/CT and FFB guided implantation groups, 88.57%(31/35) and 77.27%(51/66) were under local control respectively, and 1-year survival rates were 91.43%(32/35) and 80.30%(53/66) respectively. Radiation pneumonitis and pulmonary fibrosis were not detected in all 3 groups. Conclusion Standard application of quality assurance and quality control is the guarantee of the improvement of therapeutic gain ratio of seed implantation guided by image. Key words: Carcinoma, non-small-cell lung; Brachytherapy; Iodine radioisotopes