Correlation between average absorbed dose and metabolic response in the radio-embolization of liver colorectal metastases with resin microspheres

1237 Objectives To highlight a dose-effect relationship in the treatment of liver colorectal metastases with resin microspheres. Methods Retrospective analysis of 31 colorectal cancer (CRC) patients with liver-dominant metastases undergoing radioembolization with 90Y resin microspheres. The average absorbed doses (AAD) were calculated from the 99mTc-MAA-SPECT/CT dataset (Symbia T2, Siemens) and the 90Y injected activity. The metabolic response was calculated by the difference in total lesion glycolysis (ΔTLG) between the baseline and follow-up 18FDG-PET/CT (4 weeks posttreatment). All processing was performed with the PLANET Dose (Dosisoft, Cachan, France) software tool, i.e. tumor delineation, SUV quantification and absorbed dose calculation (dose kernel convolution). The dose-response relationship was analysed through a log function, statistical analysis included univariate and multivariate analysis. Results Four patients were excluded from analysis due to data inconsistency. The injected activity was 1368 ± 831 MBq (1 SD), the mean number and volume of assessed lesions per patient was 2.5 ± 2.3 and 289 ± 420 cm3, respectively, AAD was 89 ± 72 Gy. Multivariate analysis allowed highlighting 2 groups (G): G1 with no response and G2 with response and a log correlation between ΔTLG and AAD (ΔTLG = -4416 x ln(AAD) + 14468, r2=0,76). G1 had a mean lesion volume of 81 ± 80 cm3 versus 513 ± 520 cm3 in G2 (p=0.0057), G1 had a TLG of 501 ± 476 and G2 3553 ± 3302 (p=0.0030). G1 AAD was 129 ± 80 Gy, G2 was 47 ± 24 Gy (p=0.0011). Conclusions The results suggest a dose-response relationship in CRC liver metastases treated by 90Y-resin microspheres for lesions with a high baseline TLG.