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

Radiation pneumonitis is a serious complication of radioembolization. In holmium-166 ([¹⁶⁶Ho]) radioembolization, the lung mean dose (LMD) can be estimated (eLMD) using a scout dose with either technetium-99 m-macroaggregated albumin ([^99mTc]MAA) or [¹⁶⁶Ho]-microspheres. The accuracy of eLMD based on [^99mTc]MAA (eLMD_MAA) was compared to eLMD based on [¹⁶⁶Ho]-scout dose (eLMD_Ho-scout) in two prospective clinical studies.

Patients were included if they received both scout doses ([^99mTc]MAA and [¹⁶⁶Ho]-scout), had a posttreatment [¹⁶⁶Ho]-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.

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).

[¹⁶⁶Ho]-scout dose is superior in predicting LMD over [^99mTc]MAA, in [¹⁶⁶Ho]-radioembolization. Consequently, [¹⁶⁶Ho]-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.