Reply to "Hepatic Radioembolization as a True Single-Session Treatment"

Repeat Evaluation of Lung Shunt Fraction is Unnecessary: A Retrospective Observational Study of Successive Lung Shunt Fractions from Variable Arterial Distributions in Patients Undergoing Radioembolization of Primary and Secondary Liver Tumors

PURPOSE

To evaluate whether the recalculation of lung shunt fraction (LSF) is necessary prior to next-stage or same lobe repeat radioembolization.

MATERIALS AND METHODS

Retrospective chart review was performed for patients who underwent radioembolization between February 2008 and December 2018. Eighty of 312 patients had repeat mapping angiograms and LSF calculations. A total of 160 LSF calculations were made using planar imaging (155, [97%]) and single-photon emission computed tomography (5 [3%]) technetium-99m macroaggregated albumin hepatic arterial injection imaging. The mean patient age was 61.8 years ± 12.7; 69 (86%) patients had metastatic disease and 11 (14%) had hepatocellular carcinoma.

RESULTS

Patients had a median LSF of 5% (interquartile range [IQR] 3%-9%) with a median absolute difference of 1.25 (IQR 0.65-3.4) and a median of 76 days (IQR 42.5-120 days) between repeat LSF calculations. There was a median change in LSF of 0.2% between mapping studies (P = .11). There was no statistical significance between the repeat LSFs regardless of the arterial distribution (P = .79) or between tumor types (P = .75). No patients exceeded lung dose limits using actual or predicted prescribed dose amounts. The actual median lung dose was 2.6 Gy (IQR 1.8-4.4 Gy, maximum = 20.5) for the first radioembolization and 2.0 Gy (IQR 1.3-3.7 Gy, maximum = 10.1) for the second radioembolization.

CONCLUSIONS

No significant difference in LSF was identified between different time points and arterial distributions within the same patient undergoing repeat radioembolization. In patients who receive well under 30-Gy lung dose for the initial treatment and a 50-Gy cumulative lung dose, repeat radioembolization treatments in the same patient may not require a repeat LSF calculation.

Evaluation of the Safety and Feasibility of Same-Day Holmium-166 -Radioembolization Simulation and Treatment of Hepatic Metastases

PURPOSE

To evaluate the safety and feasibility of same-day treatment, including the simulation procedure for assessment of intrahepatic and extrahepatic distribution of the microspheres, with holmium-166 (¹⁶⁶Ho)-radioembolization.

MATERIALS AND METHODS

This was a secondary analysis of patients included in the 4 prospective studies (HEPAR I, HEPAR II, HEPAR PLuS, and SIM) on ¹⁶⁶Ho-radioembolization. The technical success rate of the same-day treatment protocol, defined as the number of patients who completed the same-day treatment, was measured. Total in-room time, duration of the scout procedure, time to imaging, and duration of the treatment procedure were recorded. Reasons for discontinuation or adjustment of treatment were identified. Adverse events that occurred during the treatment day were recorded.

RESULTS

One hundred five of 120 scheduled patients completed the same-day treatment with ¹⁶⁶Ho-radioembolization (success rate, 88%). After the simulation procedure, treatment was cancelled in 15 patients because of extrahepatic deposition (n = 8), suboptimal tumor targeting (n = 1), unanticipated vascular anatomy (n = 5), and dissection (n = 1). In another 14 patients, the treatment plan was adjusted. The median total procedure time (ie, simulation, imaging, and treatment) was 6:39 hours:minutes (range, 3:58-9:17 hours:minutes). Back pain was a major same-day treatment-related complaint (n = 28).

CONCLUSION

¹⁶⁶Ho-radioembolization as a same-day treatment procedure is feasible in most selected patients, although treatment was adjusted in 12% of patients and cancelled in 12% of patients. This approach might be beneficial for a select patient population, such as patients needing a radiation segmentectomy.

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

OBJECTIVE

Radioembolisation 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.

METHODS

All 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.

RESULTS

In 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).

CONCLUSION

These 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.

Safety of a Scout Dose Preceding Hepatic Radioembolization with 166Ho Microspheres

Before (166)Ho radioembolization, a small batch of the same type of microspheres is administered as a scout dose instead of the conventional (99m)Tc-macroaggregated albumin ((99m)Tc-MAA). The (166)Ho scout dose provides a more accurate and precise lung shunt assessment. However, in contrast to (99m)Tc-MAA, an unintended extrahepatic deposition of this β-emitting scout dose could inflict radiation damage, the extent of which we aimed to quantify in this study.

METHODS

All patients eligible for radioembolization in our institute between January 2011 and March 2014 were reviewed. Of the extrahepatic depositions of (99m)Tc-MAA on SPECT, the amount and volume were measured. These were used to calculate the theoretic absorbed dose in the case a (166)Ho scout dose had been used. The extrahepatic activity was measured as the sum of all voxels of the deposition. Volumes were measured using a threshold technique including all voxels from the maximum voxel intensity up to a certain percentage. The threshold needed to obtain the true volume was studied in a phantom study.

RESULTS

In the phantom study, a threshold of 40% was found to overestimate the volume, with the consequence of underestimating the absorbed dose. Of 160 patients, 32 patients (34 cases) of extrahepatic deposition were identified. The depositions contained a median of 1.3% (range, 0.1%-19.5%) of the administered activity in a median volume of 6.8 mL (range, 1.1-42 mL). The use of a scout dose of 250 MBq of (166)Ho microspheres in these cases would theoretically have resulted in a median absorbed dose of 6.0 Gy (range, 0.9-374 Gy). The dose exceeded a limit of 49 Gy (reported in 2013) in 2 of 34 cases (5.9%; 95% confidence interval, 0.7%-20.1%) or 2 of 160 (1.3%; 95% confidence interval, 0.1%-4.7%) of all patients. In these 2 patients with a large absorbed dose (112 and 374 Gy), the culprit vessel was identified in 1 case.

CONCLUSION

Extrahepatic deposition of a (166)Ho scout dose seems to be theoretically safe in most patients. Its safety in clinical practice is being evaluated in ongoing clinical trials.