[Article] Analysis of Differences Between 99mTc-MAASPECT- and 90Y-microsphere PET-based Dosimetry for Hepatocellular Carcinoma Selective Internal Radiation Therapy

Analysis of Differences Between ⁹⁹mTc-MAASPECT- and ⁹⁰Y-microsphere PET-based Dosimetry for Hepatocellular Carcinoma Selective Internal Radiation Therapy

Marilyne Kafrouni^1,2,3*, Carole Allimant⁴, Marjolaine Fourcade¹, Sébastien Vauclin³, Boris Guiu^2,4, Denis Mariano-Goulart^1,2, and Fayçal Ben Bouallègue^1,2

1 Department of Nuclear Medicine, Montpellier University Hospital,Montpellier, France.
2 PhyMedExp, Montpellier University, INSERM, CNRS,Montpellier, France.
3 DOSIsoft SA, Cachan, France.
4 Department of Radiology,Montpellier University Hospital, Montpellier, France

ABSTRACT
Purpose: The aim of this study was to compare predictive and post-treatment dosimetry and analyze thedifferences, investigating factors related to activity preparation and delivery, imaging modality used, andinterventional radiology.

Methods: Twenty-three HCC patients treated by selective internal radiation therapy with ⁹⁰Y glass microsphereswere included in this study. Predictive and post-treatment dosimetry were calculated at the voxel level based on ^99mTc-MAA SPECT/CT and ⁹⁰Y-microsphere PET/CT respectively. Dose distribution was analyzed through mean dose,metrics extracted from dose-volume histograms, and Dice similarity coefficients applied on isodoses. Reproducibilityof the radiological gesture and its influence on dose deviation was evaluated.

Results: ⁹⁰Y delivered activity was lower than expected in 67% (16/24) of the cases mainly due to the residualactivity. A mean deviation of−6 ± 11% was observed between the delivered activity and the90Y PET’s FOV activity.In addition, a substantial difference of−20 ± 8% was measured on ⁹⁰Y PET images between the activity in the liverand in the whole FOV. After normalization,^99mTc-MAA SPECT dosimetry was highly correlated and concordant with ⁹⁰Y-microsphere PET dosimetry for all dose metrics evaluated (ρ= 0.87,ρ_c= 0.86,P= 3.10−8 and ρ= 0.91,ρ_c= 0.90,P= 7.10−10for tumor and normal liver mean dose respectively for example). Besides, mean tumor dose deviationwas lower when the catheter position was identical than when it differed (16 Gy vs. 37 Gy,P= 0.007). Concordancebetween predictive and post-treatment dosimetry, evaluated with Dice similarity coefficients applied on isodoses,significantly correlated with the distance of the catheter position from artery bifurcation (P= 0.04, 0.0004, and 0.05,for 50 Gy, 100 Gy, and 150 Gy isodoses respectively).

Conclusion: Discrepancies between planned activity and activity measured on ⁹⁰Y PET images were observed andseemed to be mainly related to clinical hazards and equipment issues. Predictive vs. post-treatment comparison ofrelative dose distributions between tumor and normal liver showed a good correlation and no significant differencehighlighting the predictive value of ^99mTc MAA SPECT/CT-based dosimetry. Besides, the reproducibility of cathetertip position appears critical in the agreement between predictive and actual dose distribution.