The efficacy and dosimetry analysis of CT-guided 125I seed implantation assisted with 3D-printing non-co-planar template in locally recurrent rectal cancer

Background: Locally recurrent rectal cancer (LRRC) after surgery or external beam radiotherapy (EBRT) is a serious challenge for which no standard treatment is defined. In the present study, we investigated the feasibility of computed tomography (CT)-guided radioactive(125)I seed (RIS) implantation assisted with three-dimensional printing non-coplanar template (3D-PNCT) in LRRC patients who previously received surgery or EBRT. Methods: Sixty-six patients with LRRC treated by CT-guided RIS implantation in our institute from December 2015 to May 2019 were included. The treatment procedure included: preoperative CT localization, planning design, the printing of 3D individualized template, CT-guided RIS implantation assisted with 3D-PNCT, and postoperative dose evaluation. Therapeutic outcomes including local control (LC) and overall survival (OS) were retrospectively evaluated, as well as side effects. Results: All the patients had previously received surgery or EBRT. The median follow-up time was 12.2 (range, 2.5-35.9) months. The median radioactive activity of a single RIS was 0.6 (range, 0.43-0.72) mCi. The median number of RIS was 60, ranging from 10 to 175. The dosimetric parameters included D90 (140.7 +/- 33.1) Gy, D100 (90.3 +/- 138.6) Gy, and V100 (91.0 +/- 13.3) %. Pain relief was achieved in 85.1% (40/47) of patients. Besides, 9.1% (6/66) of patients had severe side effects (>= grade 3), including perianal skin ulcer in 1 case, fistula, radiation proctitis, and intestinal obstruction each in two cases. Median OS time was 14.7 (95% confidence interval (CI): 13.0-16.3) months, and median LC time was 12.2 (95% CI: 9.1-15.2) months. Univariate analysis revealed that when D90 > 130 Gy or D100 > 55 Gy or V100 > 90%, the LC time was remarkably prolonged. However, none of the parameters significantly affected OS. Conclusions: CT-guided RIS implantation assisted with 3D-PNCT is an effective and safe salvage treatment strategy for patients with LRRC after EBRT or surgery. D90, D100, and V100 can be used as prognostic predictors.