Impact of Y-90 glass microspheres residue measurement post-TARE using PET/CT on the tumor absorbed dose in comparison to planned dosimetry with Tc99m MAA scintigraphy.

Introduction: Transarterial radio-embolization (TARE) is routinely used for the treatment of non resectable liver tumor especially hepatocellular carcinoma (HCC). Recent Dosisphere-01 trial (Garin et al. 2021) showed the importance of a personalized dosimetry in HCC patients with a threshold of 205 Gy absorbed dose for the index lesion being associated with a better response rate. Yet, routine measurement of the precise activity injected during the TARE procedure are not yet standardized. In that setting, we measured the Y-90 glass microspheres residue using PET/CT after TARE to assess its impact on the tumor absorbed dose previously planned with Tc-99m-MAA scintigraphy. We also investigated which parameters might be associated with a higher Y-90 microspheres residue post-TARE.

Methods: Patients&nbsp;undergoing TARE using Y-90 glass-microspheres (TheraSphere&trade;) for non-resectable liver tumor from February 2021 to December 2021 were included in this retrospective, single-centered study. Y-90 glass microspheres &ldquo;&nbsp;residue&rdquo;&nbsp;consisting of the Theraspheres vial and the microcatheter used for the injection were imaged post-TARE on PET/CT scanner (Biograph VISION 600-Siemens). We assessed the residue post-TARE in percentage of the activity measured in the TheraSphere&trade; vial before TARE. We used t-test for dependent samples to compare perfused volume and perfused tumor absorbed doses before (as estimated on Tc99m MAA scintigraphy) and after applying the post-TARE residue. We used Mann-Whitney test to compare the value of the&nbsp;residue according to&nbsp;the type of microcatheter (Terumo Progreat 2.7Fr. Microcatheter (PG) vs ASAHI Parkway Soft 1,98 F microcatheter (AP)), the type of treatment (radiation segmentectomy versus partition) and&nbsp;the size of the perfused volume (large&nbsp;&ge;400cm^3&nbsp;versus small <400 cm³). We used Anova test to compare&nbsp;the value of the&nbsp;residue according to the arterial position for&nbsp;TARE (lobar artery versus sectorial hepatic branch versus segmental hepatic branch). Pearson correlation was used to assess the association between the residue in percent and perfused volume, tumor perfused volume and the&nbsp;activity measured in the&nbsp;TheraSphere&trade; vial before TARE.

Results: Twenty-five patients (20 HCC pts) with a total of 43 injections were included. The mean value for the post-TARE residue measured on PET/CT was 92MBq±86 [2-406] corresponding to a mean percent value of 5.5%±4.5 [0.2-18.9%] in comparison to the Activity measured in the TheraSphere&trade; vial before TARE (1939MBq± 1250 [542-6269]). There were significant differences in the absorbed dose values in comparison with the planned dosimetry of Tc-99m-MAA scintigraphy&nbsp;for the perfused volume ( 270Gy±217 post-TARE versus&nbsp;290Gy±232&nbsp;; p<0.0001) and perfused tumor (375Gy±382 post-TARE versus&nbsp;395Gy±397; p=0.001). We found a borderline significant difference&nbsp;according to the type of microcatheter used during &nbsp;TARE with smaller microcatheter having higher Y90 glass microspheres &laquo;&nbsp;residu&nbsp;&raquo; values&nbsp; (6.9%±4.7 (AP) versus 4.6%±2.3 (PG) ; p=0.06). By contrast, there were no significant difference according to the type of treatment, the size of the perfused volume&nbsp;or the arterial position for TARE . Similarly, there was no significant correlation between the residue in percent with the perfused volume, the tumor perfused volume or the activity measured in the&nbsp;TheraSphere&trade; vial before TARE.

Conclusions: We reported our preliminary results measuring Y-90 glass microspheres residue post-TARE in a small cohort of patients with a mean residue below 10%. Yet, after applying&nbsp;this residue to the planned dosimetry on the Tc-99m-MAA scintigraphy we found significant differences with post-TARE absorbed doses for the perfused volume and the perfused tumor. It might have to be accounted for in patients with borderline dosimetry on the Tc-99m-MAA scintigraphy with an absorbed dose for the index lesion&nbsp;slitghly above the 205 Gy threshold. We also, found a trend for smaller microcatheter to retain higher Y-90 glass microspheres and thus&nbsp;higher&nbsp;residue.