Clinical and imaging-based prognostic factors in radioembolisation of liver metastases from colorectal cancer: a retrospective exploratory analysis

BACKGROUND The aim of this study was to investigate the relationship between absorbed dose and response of colorectal cancer liver metastases treated with [90Y]-resin microspheres and to explore possible clinical and imaging derived prognostic factors. METHODS FDG PET/CT was used to measure response of individual lesions to a measured absorbed dose, derived from post-treatment 90Y PET imaging. Predicted dose was also derived from planning [99mTc]-MAA SPECT data. Peak standardised uptake value and total lesion glycolysis (TLG) were explored as response measures, and compared to dose metrics including average dose (D avg), biologically effective dose, minimum dose to 70% of lesion volume and volume receiving at least 50 Gy. Prognostic factors examined included baseline TLG, RAS mutation status, FDG heterogeneity and dose heterogeneity. In an exploratory analysis, response and clinico-pathological variables were evaluated and compared to overall survival. RESULTS Sixty-three lesions were analysed from 22 patients. Poor agreement was seen between predicted and measured dose values. TLG was a superior measure of response, and all dose metrics were significant prognostic factors, with a D avg of ~50 Gy derived as the critical threshold for a significant response (>50% reduction in TLG). No significant correlation was found between baseline TLG or RAS mutation status and response. Measured dose heterogeneity was a significant prognostic factor and when combined with D avg had a positive predictive value for response >80%. In the exploratory analysis for prognostic factors of survival, low hepatic tumour burden and mean reduction in TLG >65% were independently associated with improved overall survival. CONCLUSIONS Lesions receiving an average dose greater than 50 Gy are likely to have a significant response. For lesions receiving less than 50 Gy, dose heterogeneity is a significant prognostic factor. Lesions receiving an average dose less than 20 Gy are unlikely to respond. A reduction in TLG may be associated with improved overall survival.