Dosimetry analysis of radioactive seed implantation supported by coplanar template for lung cancer patients with mediastinal lymph node metastases 4R

Objective To compare the planned radiation dose and the actual dose received after 125I radioactive seeds implantation supported by coplanar template (CPT) in lung cancer patients with mediastinal node metastases 4R, and to evaluate the clinical efficacy. Methods Totally 32 patients with lung cancer with mediastinal lymph node metastases 4R who had been diagnosed via cellular pathology studies were selected from January 2008 to December 2014. The mediastinal lymph node metastases were treated by CPT-assisted 125I radioactive seed implantation. Digital imaging and communications in medicine(DICOM) data were acquired by chest CT scan before implantation, brachytherapy radiation treatment planning system (BTPS) was introduced to carry out the plan, and the prescribed dose(PD) was 120 Gy. CPT was used to control the precision of needle penetration and implantation of radioactive seeds. Computer tomography (CT) was used to ensure the correct position of needles and radioactive seeds. Dose evaluation was performed immediately after implantation and was compared with planned dose using paired t-test. The 6-months postoperative chest CT was conducted to evaluate treatment efficacy according to response evaluation criteria in solid tumors(RECIST Version 1.1). Results All patients went through implantation procedure successfully. Dose evaluation after implantation was as followed. The average dose received (231.9±29.6)Gy, the dose received by 90% of the target(D90) (150.8±16.6) Gy, the dose received by 100% of the target(D100) (100.4±12.6)Gy, the volume of 100%PD covering the target(V100) (94.1±2.6)%, the volume of 200%PD covering the target(V200) (33.0±5.7)%, the conformal index(CI) 0.75±0.06, the external index(EI) (22.7±5.8)%, the average dose received by the superior vena cava (19.3±7.2)Gy, and the average dose received by aorta (12.1±5.1)Gy. Efficacy was followed for 6 months after implantation and the effective rate was 84.37%. There was no serious complications (such as radioactive lung injury, major vascular injury, bleeding, and et al.) occurred in follow-up period. Conclusions CPT assisted CT guided 125I radioactive seed implantation in treating mediastinal node metastases 4R can achieve preoperative BTPS, minimize major vascular or organ injury. It is an accurate, effective and safe treatment approach and may be of great value to standardize the procedure of radioactive seed implantation in mediastinal metastases. Key words: CT guided; Coplanar template; Radioactive seeds; Brachytherapy treatment planning system; Mediastinal lymph node metastasis