Dosimetry, efficacy, and safety of three-dimensional printing noncoplanar template-assisted and CT-guided 125I seed implantation for recurrent retroperitoneal lymphatic metastasis after external beam radiotherapy

Objectives To evaluate the dosimetry, efficacy, and safety of radioactive 125I seed implantation (RISI) assisted by three-dimensional printing noncoplanar template (3D-PNCT) and CT for recurrent retroperitoneal lymphatic metastasis (RRLM) after previous external beam radiotherapy. Methods and Materials From June 2016 to August 2018, 32 patients with RRLM successfully underwent 3D-PNCT–assisted and CT-guided RISI. The dosimetry, pain relief rate, performance improvement rate, overall response rate, disease control rate, local control time (LCT), overall survival (OS), and safety profiles were evaluated. Results Dosimetric results showed that the D90, D100, V100, V150, V200, and homogeneity index were consistent in preoperation and postoperation (p > 0.05), except for the external index and conformal index (p = 0.048, p = 0.034). After RISI, 81.3% of the patients achieved pain relief, and 71.9% achieved an improvement of performance. The overall response rate and disease control rate were 85.3% and 94.1%, respectively. The LCT rates reached 66.2% and 43.2% in 1 year and two years, respectively, with a median LCT of 15.8 months. The OS rates were 74.1% and 28.1% in 1 year and two year, respectively, with a median OS reaching 17.6 months. Univariate analysis showed that when D90 > 130 Gy or D100 > 63 Gy or tumor size ≤49.8 cm3, LCT was extended significantly, but not for OS. Except for two patients developing Grade 1 retroperitoneal hematomas, no other severe adverse events were observed. Conclusions 3D-PNCT and CT guidance provide excellent accuracy for RISI, which can be an effective and safe alternative for RRLM after external beam radiotherapy. Radiation dose and tumor size seem to significantly influence the local control.