[Article] 90Y-PET/CT-based Dosimetry after Selective Internal Radiation Therapy Predicts Outcome in Patients with Liver Metastases from Colorectal Cancer

⁹⁰Y-PET/CT-based dosimetry after selective internal radiation therapy predicts outcome in patients with liver metastases from colorectal cancer

Hugo Levillain^1* , Ivan Duran Derijckere¹, Gwennaëlle Marin², Thomas Guiot¹, Michaël Vouche³, Nick Reynaert², Alain Hendlisz⁴, Bruno Vanderlinden² and Patrick Flamen¹
1 Department of Nuclear Medicine, Jules Bordet Institute, Université Libre de Bruxelles, Rue Héger-Bordet 1, B-1000, Brussels, Belgium.
2 Department of Medical Physics, Jules Bordet Institute, Université Libre de Bruxelles, Rue Héger-Bordet 1, B-1000, Brussels, Belgium.
3 Department of Radiology, Hôpital St-Pierre, Jules Bordet Institute, Université Libre de Bruxelles, Rue Héger-Bordet 1, B-1000, Brussels, Belgium.
4 Department of Digestive Oncology, Jules Bordet Institute, Université Libre de Bruxelles, Rue Héger-Bordet 1, B-1000, Brussels, Belgium.

ABSTRACT
Background: The aim of this work was to confirm that post-selective internal radiation therapy (SIRT) ⁹⁰Y-PET/CTbased dosimetry correlates with lesion metabolic response and to determine its correlation with overall survival (OS) in liver-only metastases from colorectal cancer (mCRC) patients treated with SIRT. Twenty-four mCRC patients underwent pre/post-SIRT FDG-PET/CT and post-SIRT ⁹⁰Y-PET/CT. Lesions delineated on pre/post-SIRT FDG-PET/CT were classified as non-metabolic responders (total lesion glycolysis (TLG)-decrease < 15%) and high-metabolic responders (TLG-decrease ≥ 50%). Lesion delineations were projected on the anatomically registered ⁹⁰Y-PET/CT. Voxel-based 3D dosimetrywas performed on the ⁹⁰Y-PET/CT and lesions’ mean absorbed dose (Dmean) was measured. The coefficient of correlation between Dmean and TLG-decrease was calculated. The ability of lesion Dmean to predict non-metabolic response and high-metabolic response was tested and two cutoff values (Dmean-under-treated and Dmean-well-treated) were determined using ROC analysis. Patients were dichotomised in the “treated” group (all the lesions received a Dmean > Dmean-under-treated) and in the “under-treated” group (at least one lesion received a Dmean < Dmean-under-treated). Kaplan-Meier product limit method was used to describe OS curves.

Results: Fifty-seven evaluable mCRC lesions were included. The coefficient of correlation between Dmean and TLGdecrease was 0.82. Two lesion Dmean cutoffs of 39 Gy (sensitivity 80%, specificity 95%, predictive-positive-value 86% and negative-predictive-value 92%) and 60 Gy (sensitivity 70%, specificity 95%, predictive positive-value 96% and negative-predictive-value 63%) were defined to predict non-metabolic response and high-metabolic response respectively. Patients with all lesions Dmean> 39 Gy had a significantly longer OS (13 months) than patients with at
least one lesion Dmean < 39 Gy (OS = 5 months) (p = 0.012;hazard-ratio, 2.6 (95% CI 0.98–7.00)).

Conclusion: In chemorefractory mCRC patients treated with SIRT, lesion Dmean determined on post-SIRT ⁹⁰Y-PET/CT correlates with metabolic response and higher lesion Dmean is associated with prolonged OS.