166Ho-RadioEmbolizaTiOn Using personalized prediCtive dosimetry in patients with Hepatocellular carcinoma: A prospective, single-centre study (RETOUCH).

Background and aims: Holmium-166 (¹⁶⁶Ho) radioembolization could offer a more individualized approach in terms of imaging and dosimetry. We aim to evaluate the feasibility and safety of ¹⁶⁶Ho selective internal radiation therapy (SIRT) using a higher tumour dose than previously administered determined by ¹⁶⁶Ho-scout as a surrogate marker in HCC patients.

Methods: This is an open-label, prospective, non-randomized, single-centre pilot study that included patients with HCC that received ¹⁶⁶Ho-SIRT if the work-up using ¹⁶⁶Ho-scout showed a tumour-absorbed dose ≥150 Gy, a non-tumoural liver absorbed dose less than 60 Gy and a lung absorbed dose less than 30 Gy. Primary endpoints were feasibility and safety-toxicity profiles at 24-48 h and 1 month. Overall response rates (ORR) at 3 months (mRECIST, RECIST 1.1 and metabolic response by FDG and choline PET CT) and time to progression (TTP) represented the secondary endpoints.

Results: Fifteen patients with large tumours (mean diameter 55.67 ± 28.42 mm) received 17 ¹⁶⁶Ho-SIRT treatments between July 2020 and June 2022. All the attempted treatments were accomplished. Mean administered tumour dose was 183.18 ± 71.71 Gy, while non-tumour liver dose was 30.29 ± 14.56 Gy. Median time of follow-up was 12 months (IQR 9-16). Only grade 1-2 clinical and biological AEs were observed. There were no liver decompensations. At 3 months, objective response was achieved for all target lesions (CR 78.57%, PR 21.43% according to mRECIST). Median TTP was 18.8 (range 2.9; n.e.) months.

Conclusion: Personalized ¹⁶⁶Ho-SIRT with a tumour delivered dose ≥150 Gy was feasible and safe for HCC patients with promising response rates.