Needle track seeding in colorectal carcinoma after local ablation by high-dose-rate brachytherapy: a retrospective study of 1,107 catheter placements

Purpose
Image-guided brachytherapy with a single-fraction irradiation (high-dose-rate brachytherapy – HDR-BT) is a promising local ablation technique for unresectable liver metastases. The occurrence of needle track seeding after biopsy and microwave ablation (MWA) has been documented primarily in hepatocellular carcinoma (HCC). Comprehensive data on colorectal metastases and treatment with HDR-BT is missing. The aim of this study was to investigate the incidence of extra- and intra-hepatic track seeding after HDR-BT in patients with colorectal metastases of the liver, and the identification of possible risk factors.

Material and methods
Patients with at least one treatment of HDR-BT were included. Two readers identified possible track seeding after at least 3 months of follow-up. For verification, we used image fusion of CT/MRI images from 3D irradiation plan and follow-up. Intra- and extra-hepatic seeding were included. As possible risk factors, demographics, tumor grading, and aspects of catheter placement were identified, and generalized linear mixed model for evaluation was applied.

Results
On total, 138 patients were included in the study (85 males). We treated 472 liver lesions with 1,107 catheter placements. Sixteen needle track lesions were identified with a catheter-based risk of 1.5% and patient-based risk of 10.9% during a median follow-up of 543 days. Extra-hepatic track seeding (patient-based risk of 1.4%) was found in two patients only. Possible risk factors were tumor grading (p = 0.01) and using MRI-guidance (p = 0.02). There was also a correlation with a high number of interventions per patient (p = 0.009) and number of treated lesions (p = 0.04).

Conclusions
Brachytherapy for treatment of colorectal metastases is associated with a similar risk for extra-hepatic track seeding compared to radio-frequency ablation (RFA). Intra-hepatic seeding, which has not been studied extensively before, occurs more often with seeding frequency comparable to biopsy of colorectal metastases. Possible risk factors could be tumor grading and using MRI-guidance.