RT Journal Article SR Electronic T1 First Evidence for a Dose–Response Relationship in Patients Treated with 166Ho Radioembolization: A Prospective Study JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 608 OP 612 DO 10.2967/jnumed.119.232751 VO 61 IS 4 A1 Remco Bastiaannet A1 Caren van Roekel A1 Maarten L.J. Smits A1 Sjoerd G. Elias A1 Wouter A.C. van Amsterdam A1 Dan Doan A1 Jip F. Prince A1 Rutger C.G. Bruijnen A1 Hugo W.A.M. de Jong A1 Marnix G.E.H. Lam YR 2020 UL http://jnm.snmjournals.org/content/61/4/608.abstract AB 166Ho-microspheres have recently been approved for clinical use for hepatic radioembolization in the European Union. The aim of this study was to investigate the absorbed dose–response relationship and its association with overall survival for 166Ho radioembolization in patients with liver metastases. Methods: Patients treated in the HEPAR I and II studies who underwent an 18F-FDG PET/CT scan at baseline, a posttreatment 166Ho SPECT/CT scan, and another 18F-FDG PET/CT scan at the 3-mo follow-up were included for analysis. The posttreatment 166Ho-microsphere activity distributions were estimated with quantitative SPECT/CT reconstructions using a quantitative Monte Carlo–based method. The response of each tumor was based on the change in total lesion glycolysis (TLG) between baseline and follow-up and was placed into 1 of 4 categories, according to the PERCIST criteria, ranging from complete response to progressive disease. Patient-level response was grouped according to the average change in TLG per patient. The absorbed dose–response relationship was assessed using a linear mixed model to account for correlation of tumors within patients. Median overall survival was compared between patients with and without a metabolic liver response, using a log-rank test. Results: Thirty-six patients with a total of 98 tumors were included. The relation between tumor-absorbed dose and both tumor-level and patient-level response was explored. At a tumor level, a significant difference in geometric mean absorbed dose was found between complete response (232 Gy; 95% confidence interval [CI], 178–303 Gy; n = 32) and stable disease (147 Gy; 95% CI, 113–191 Gy; n = 28) (P = 0.01) and between complete response and progressive disease (117 Gy; 95% CI, 87–159 Gy; n = 21) (P = 0.0008). This constitutes a robust absorbed dose–response relationship. At a patient level, a significant difference was found between patients with complete or partial response (210 Gy; 95% CI, 161–274 Gy; n = 13) and patients with progressive disease (116 Gy; 95% CI, 81–165 Gy; n = 9) (P = 0.01). Patients were subsequently grouped according to their average change in TLG. Patients with an objective response (complete or partial) exhibited a significantly higher overall survival than nonresponding patients (stable or progressive disease) (median, 19 mo vs. 7.5 mo; log-rank, P = 0.01). Conclusion: These results confirm a significant absorbed dose–response relationship in 166Ho radioembolization. Treatment response is associated with a higher overall survival.