In-depth clinical and dosimetric analysis of Ho-radioembolization in patients with liver cancer: An observational study.

[INTRODUCTION] Transarterial radioembolization (TARE) using holmium-166 (¹⁶⁶Ho) microspheres is a treatment for unresectable primary and secondary liver malignancies. The pre-therapeutic simulation procedure using a scout dose is critical to predict microsphere distribution and exclude extrahepatic leakage. This single-center observational study aimed to evaluate the dosimetric agreement between ¹⁶⁶Ho-scout and ¹⁶⁶Ho-therapy, and to correlate tumor-absorbed dose with treatment response at both tumor and patient levels.

[METHODS] Prospective, observational study included patients with BCLC 2022 stage A/B hepatocellular carcinoma or oligometastatic liver disease undergoing ¹⁶⁶Ho-TARE were included. Voxel-based dosimetry was performed using Q-suite. Contrast-enhanced CT was acquired 3 months post-treatment. Treatment response was assessed by RECIST/mRECIST criteria.

[RESULTS] Twenty patients underwent the pre-treatment procedure; 18 proceeded to therapy. No significant differences were observed between scout and therapy procedures in whole-liver (P=.331) and tumor doses (P=.063), indicating reliable pre-therapeutic evaluation. Fourteen patients with 16 treated lesions were included in the dose-response analysis (median volume: 22,1 [10,5-80,3]mL; dose: 22,1 [10,5-80,3]Gy). The objective tumor response rate at 3 months was 94%. However, no significant differences were found in absorbed dose metrics (P=.315) or dose-volume histogram values (D50, D70, D85) between responsive and non-responsive (NR) lesions. Patient-level analysis showed a 29% progression rate, with NR patients more likely to have secondary liver tumors (P=.011).

[CONCLUSION] This study including a Portuguese cohort treated with ¹⁶⁶Ho-TARE showed a high tumor response rate. However, the limited sample size reduces the robustness of the conclusions. Further data from ongoing follow-up are awaited.