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 for99mTc-MAA for radioembolisation work-up.• Holmium-166 scout dose potentially has several benefits over99mTc-MAA for radioembolisation work-up.
Highlights
Before yttrium-90 (90Y) radioembolisation (RE) is performed, a scout dose is used to predict intra- and extrahepatic distribution of activity and check for potential contraindications
In patients treated with holmium-166 (166Ho) microspheres a scout dose using 250 MBq 166Ho is used as an alternative, which is superior in calculating the lung shunt fraction compared to 99mTcMAA [1]
All patients included in this study participated in a prospective trial with 166Ho microspheres (Table 1 [4,5,6,7]) and written informed consent was obtained for all patients at study inclusion
Summary
Before yttrium-90 (90Y) radioembolisation (RE) is performed, a scout dose is used to predict intra- and extrahepatic distribution of activity and check for potential contraindications (i.e. excessive lung shunt and extrahepatic depositions). In patients treated with holmium-166 (166Ho) microspheres a scout dose using 250 MBq 166Ho is used as an alternative, which is superior in calculating the lung shunt fraction compared to 99mTcMAA [1]. This may be due to the fact that identical 166Ho microspheres are used for the scout dose procedure and the RE treatment. An earlier study concluded that 166Ho microspheres can safely replace 99mTc-MAA in the majority of cases [3]. These data were based on 99mTc-MAA data of extrahepatic depositions, theoretically translated to 166Ho microspheres; if these extrahepatic 99mTc-MAA
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