Safety analysis of holmium-166 microsphere scout dose imaging during radioembolisation work-up: A cohort study

Abstract

ObjectiveRadioembolisation is generally preceded by a scout dose of technetium-99m-macroaggregated albumin to estimate extrahepatic shunting of activity. Holmium-166 microspheres can be used as a scout dose (±250 MBq) and as a therapeutic dose. The general toxicity of a holmium-166 scout dose (166Ho-SD) and safety concerns of an accidental extrahepatic deposition of 166Ho-SD were investigated.MethodsAll patients who received a 166Ho-SD in our institute were reviewed for general toxicity and extrahepatic depositions. The absorbed dose in extrahepatic tissue was calculated on SPECT/CT and correlated to clinical toxicities.ResultsIn total, 82 patients were included. No relevant clinical toxicity occurred. Six patients had an extrahepatic deposition of 166Ho-SD (median administered activity 270 MBq). The extrahepatic depositions (median activity 3.7 MBq) were located in the duodenum (3x), gastric fundus, falciform ligament and the lesser curvature of the stomach, and were deposited in a median volume of 15.3 ml, which resulted in an estimated median absorbed dose of 3.6 Gy (range 0.3–13.8 Gy). No adverse events related to the extrahepatic deposition of the 166Ho-SD occurred after a median follow-up of 4 months (range 1–12 months).ConclusionThese results support the safety of 250 MBq 166Ho-SD in a clinical setting.Key Points• A holmium-166 scout dose is safe in a clinical setting. • Holmium-166 scout dose is a safe alternative for 99m Tc-MAA for radioembolisation work-up. • Holmium-166 scout dose potentially has several benefits over 99m Tc-MAA for radioembolisation work-up.

Radioembolization lung shunt estimation based on a 90Y pretreatment procedure: A phantom study

“…Because of the low incidence of extrahepatic deposition of activity, no dose‐effect relationships have been established, but the general consensus is that absorbed doses in abdominal organs are safe up to approximately 50 Gy . Based on the empirically proven safety of a 166 Ho pretreatment procedure using 250 MBq, and the fact that 90 Y has a 3.11 times higher energy deposition compared to 166 Ho, theoretically, a lower activity for the 90 Y pretreatment procedure should be used . That would result in a 90 Y activity of around 80–100 MBq, which is above the threshold for accurate LSF estimation using Bremsstrahlung SPECT/CT when reconstructed with an MC‐based reconstruction model.…”

Simultaneous 166Ho/99mTc dual-isotope SPECT with Monte Carlo-based downscatter correction for automatic liver dosimetry in radioembolization

“…To bring pre-treatment dosimetry to a higher level, a more practical imaging protocol and a more predictive particle are needed. In previous studies, the use of a small amount of 166 Ho microspheres with an activity of 250 MBq, was determined to be safe and superior to 99m Tc-MAA [15][16][17][18][19]. Thus the main aim of this study was to investigate the technical feasibility of a dual-isotope protocol combining 166 Ho microspheres and 99m Tc sulfur colloid.…”

Feasibility of imaging 90Y microspheres at diagnostic activity levels for hepatic radioembolization treatment planning

“…Observed differences in 99m Tc‐MAA and 90 Y‐microsphere distributions could be caused by their differences in shape and size and by free circulating pertechnetate . A better representation of the microsphere distribution may be achieved by using identical particles for pretreatment and treatment, as is feasible in 166 Ho microsphere radioembolization …”

“…[7][8][9] A better representation of the microsphere distribution may be achieved by using identical particles for pretreatment and treatment, as is feasible in 166 Ho microsphere radioembolization. 10,11 A similar objective may be pursued for 90 Y-loaded microspheres. However, the total energy absorbed per Bq is higher for 90 Y than for 166 Ho, which limits the pretreatment activity to the estimated safety threshold of 100 MBq.…”