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. 2020 Apr;47(4):798-806.
doi: 10.1007/s00259-019-04460-y. Epub 2019 Aug 9.

The superior predictive value of 166Ho-scout compared with 99mTc-macroaggregated albumin prior to 166Ho-microspheres radioembolization in patients with liver metastases

Maarten L J Smits  1 , Mathijs G Dassen  1 , Jip F Prince  1 , Arthur J A T Braat  1 , Casper Beijst  1 , Rutger C G Bruijnen  1 , Hugo W A M de Jong  1 , Marnix G E H Lam  2
Affiliations

The superior predictive value of 166Ho-scout compared with 99mTc-macroaggregated albumin prior to 166Ho-microspheres radioembolization in patients with liver metastases

Maarten L J Smits et al. Eur J Nucl Med Mol Imaging. 2020 Apr.

Abstract

Purpose: As an alternative to technetium-99m-macroaggregated albumin (99mTc-MAA), a scout dose of holmium-166 (166Ho) microspheres can be used prior to 166Ho-radioembolization. The use of identical particles for pre-treatment and treatment procedures may improve the predictive value of pre-treatment analysis of distribution. The aim of this study was to analyze the agreement between 166Ho-scout and 166Ho-therapeutic dose in comparison with the agreement between 99mTc-MAA and 166Ho-therapeutic dose.

Methods: Two separate scout dose procedures were performed (99mTc-MAA and 166Ho-scout) before treatment in 53 patients. First, qualitative assessment was performed by two blinded nuclear medicine physicians who visually rated the agreement between the 99mTc-MAA, 166Ho-scout, and 166Ho-therapeutic dose SPECT-scans (i.e., all performed in the same patient) on a 5-point scale. Second, agreement was measured quantitatively by delineating lesions and normal liver on FDG-PET/CT. These volumes of interest (VOIs) were co-registered to the SPECT/CT images. The predicted absorbed doses (based on 99mTc-MAA and 166Ho-scout) were compared with the actual absorbed dose on post-treatment SPECT.

Results: A total of 23 procedures (71 lesions, 22 patients) were included for analysis. In the qualitative analysis, 166Ho-scout was superior with a median score of 4 vs. 2.5 for 99mTc-MAA (p < 0.001). The quantitative analysis showed significantly narrower 95%-limits of agreement for 166Ho-scout in comparison with 99mTc-MAA when evaluating lesion absorbed dose (- 90.3 and 105.3 Gy vs. - 164.1 and 197.0 Gy, respectively). Evaluation of normal liver absorbed dose did not show difference in agreement between both scout doses and 166Ho-therapeutic dose (- 2.9 and 5.5 Gy vs - 3.6 and 4.1 Gy for 99mTc-MAA and 166Ho-scout, respectively).

Conclusions: In this study, 166Ho-scout was shown to have a superior predictive value for intrahepatic distribution in comparison with 99mTc-MAA.

Keywords: Dosimetry; Holmium-166 microspheres; Radioembolization; SIRT; Technetium-99m-MAA.

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Conflict of interest statement

The Department of Radiology and Nuclear Medicine of the UMC Utrecht receives royalties and research support from Quirem Medical and Terumo. Marnix Lam is a consultant for BTG, Terumo and Quirem Medical. Maarten Smits has served as a speaker for Sirtex Medical, BTG and Terumo. Arthur Braat has served as a speaker for Sirtex Medical and Terumo. All other authors declare to have no conflicts of interest.

Figures

Fig. 1
Fig. 1
Example of liver and tumor segmentation on FDG-PET (a) and co-registration on 99mTc-MAA (b), 166Ho-scout (c), and 166Ho-therapeutic dose (d) SPECT images. The delineated VOIs were extended with a margin of 1 cm; therefore, each target volume is surrounded by a second line
Fig. 2
Fig. 2
Inclusion flowchart of patient data
Fig. 3
Fig. 3
Box plot. Scores of the overall agreement between both 99mTc-MAA and 166Ho-scout and 166Ho-therapeutic dose of all 23 procedures are plotted in a box plot. Median and interquartile lines are indicated. Holmium scout dose performs significantly better than 99mTc-MAA (p < 0.001)
Fig. 4
Fig. 4
Example of discrepancy between 99mTc-MAA and 166Ho-therapeutic dose. Despite identical catheter positions (upper row), there is a remarkable difference in activity distribution between the three procedures. SPECT-CT (middle and lower row) shows that the activity distribution in the liver of 166Ho-scout is more similar to the therapy distribution than 99mTc-MAA. Overall agreement of 99mTc-MAA was rated 2.5 compared to 4.5 for 166Ho scout for this patient
Fig. 5
Fig. 5
Bland-Altman plots for lesion analyses. (1) Difference between 99mTc-MAA and 166Ho-therapeutic dose activity in each lesion is plotted against mean activity in each lesion. (2) Difference between 166Ho-scout and 166Ho-therapeutic dose activity in each lesion is plotted against mean activity in each lesion. The 95% limits of agreement (LoA) are indicated and surrounded by two dotted lines indicating the standard error of the 95% LoA
Fig. 6
Fig. 6
Bland-Altman plots for healthy-liver segmentation. (1) Difference between 99mTc-MAA and 166Ho-therapeutic dose activity is plotted against mean activity for each procedure. (2) Difference between 166Ho-scout and 166Ho-therapeutic dose activity is plotted against mean activity for each procedure. The 95% limits of agreement (LoA) are indicated and surrounded by two dotted lines indicating the standard error of the 95% LoA
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