Lung Mean Dose Prediction in Transarterial Radioembolization (TARE): Superiority of [ 166 Ho]-Scout Over [ 99m Tc]MAA in a Prospective Cohort Study

Purpose Radiation pneumonitis is a serious complication of radioembolization. In holmium-166 ([ 166 Ho]) radioembolization, the lung mean dose (LMD) can be estimated (eLMD) using a scout dose with either technetium-99 m-macroaggregated albumin ([ 99m Tc]MAA) or [ 166 Ho]-microspheres. The accuracy of eLMD based on [ 99m Tc]MAA (eLMD MAA ) was compared to eLMD based on [ 166 Ho]-scout dose (eLMD Ho-scout ) in two prospective clinical studies. Materials and Methods Patients were included if they received both scout doses ([ 99m Tc]MAA and [ 166 Ho]-scout), had a posttreatment [ 166 Ho]-SPECT/CT (gold standard) and were scanned on the same hybrid SPECT/CT system. The correlation between eLMD MAA /eLMD Ho-scout and LMD Ho-treatment was assessed by Spearman’s rank correlation coefficient ( r ). Wilcoxon signed rank test was used to analyze paired data. Results Thirty-seven patients with unresectable liver metastases were included. During follow-up, none developed symptoms of radiation pneumonitis. Median eLMD MAA (1.53 Gy, range 0.09–21.33 Gy) was significantly higher than median LMD Ho-treatment (0.00 Gy, range 0.00–1.20 Gy; p < 0.01). Median eLMD Ho-scout (median 0.00 Gy, range 0.00–1.21 Gy) was not significantly different compared to LMD Ho-treatment ( p > 0.05). In all cases, eLMD MAA was higher than LMD Ho-treatment ( p < 0.01). While a significant correlation was found between eLMD Ho-scout and LMD Ho-treatment ( r = 0.43, p < 0.01), there was no correlation between eLMD MAA and LMD Ho-treatment ( r = 0.02, p = 0.90). Conclusion [ 166 Ho]-scout dose is superior in predicting LMD over [ 99m Tc]MAA, in [ 166 Ho]-radioembolization. Consequently, [ 166 Ho]-scout may limit unnecessary patient exclusions and avoid unnecessary therapeutic activity reductions in patients eligible for radioembolization. Trail registration : NCT01031784, registered December 2009. NCT01612325, registered June 2012. Graphical Abstract