99. Absorbed dose correlates with metabolic response to radioembolization of liver metastases with resin 90Y-microspheres

Abstract

Purpose To investigate possible correlation between absorbed dose (AD) and tumour response by means of Tumour Control Probability (TCP) in liver metastases treated with radioembolization (RE) with resin 90Y-microspheres. To assess response, the analysis of parameters from FDG-PET/CT has been preferred to RECIST criteria as metabolic response has proven to anticipate morphologic response. Methods Patients with chemo-refractory liver metastases from solid tumours scheduled to receive RE underwent FDG-PET/CT scan before and 6 weeks after RE. 99mTc-MAA (75–111 MBq) were injected 2 weeks before RE to perform dosimetry based on SPECT fused to contrast CT. Response assessment was based on PERCIST criteria. Variation (%) of PET parameters versus basal examination were evaluated to establish Complete-Response (CR), Partial-Response (PR), Stable-Disease (SD), Progressive-Disease (PD). Results 22 patients with hepatic lesions from colon-rectal (11), breast (7), ovary (1), endometrial (1), parotid (1) cancer, cholangiocarcinoma (1) were suitable for analysis. All patients received a single RE treatment (median activity: 1.7 GBq; range: 0.6–2.9 GBq). Median (range) tumour AD: 100(30–443) Gy. Metabolic response rate of lesions based on PERCIST were: CR = 31%; PR = 28%; SD = 24%; PD = 17%. Two different TCP curves were obtained by probit regression when considering: i) endpoint-1: PR or CR; ii) endpoint-2: CR only (p = 220 Gy only CR were observed. TCP of 50%, 75%, 100% were obtained at: i) 108, 120, 165 Gy; ii) 135, 160, 225 Gy. Conclusions Despite the variety of primary tumours, relatively low cohort of patients, and uncertainty of dosimetry with 99mTc-MAA, our preliminary data provided evidence of correlation between response based on PET/CT and AD. These encouraging results need to be confirmed with more ample dataset and, possibly, tumour type differentiation. Other PET/CT parameters such as the metabolic tumour volume and tumour lesion glycolysis are being considered for comparison with PERCIST and possible improved correlations.