title: A descriptive analysis of remnant activity during (90)Y resin microspheres radioembolization of hepatic tumors: technical factors and dosimetric implications.
abstract: OBJECTIVE
  Activity planning for (90)Y radioembolization aims to maximize the effect of the treatment while keeping toxicity acceptably low. Our aim was to describe the amount of residual activity in post-treatment v-vials and tubing and analyze the possible factors affecting it (total activity administered, number of split activity injection(s), previous treatments, administration artery and microcatheter size), as these may influence dosimetric planning and treatment.
  
  
  METHODS
  This was a retrospective review using case records of patients who received (90)Y-radioembolization for hepatic tumors at a single tertiary center. From August 2013 to September 2015, seventy-seven out of one hundred and fifty patients who received radioembolization with (90)Y resin microspheres due to inoperable Hepatocellular Carcinoma (HCC) or liver metastases were included. The rest were mainly excluded due to incomplete data sets. The number of split activities (injections) for the radioembolization could be: one single injection, two or three. The remnant activity in post-treatment v-vials and tubing were measured for every patient. The administration arteries evaluated were: proper hepatic artery (PHA), right hepatic artery (RHA), middle hepatic artery (MHA), left hepatic artery (LHA) and small caliber branch arteries. The sizes of the microcatheters (2.2 or 2.7 Fr) used to administer the dose were also evaluated.
  
  
  RESULTS
  In total, 77 out of 150 patients were included in the final analysis. There were 59 men of median age 64.0 years old. The total median dose loss was 0.10 GBq. The total dose loss increased 0.244 GBq [95 % CI = (0.169, 0.318)] when three split activities were given compared to single activity injection. Activity loss for each injection increased 0.0297 GBq [95 % CI = (0.0151, 0.0443)] for every 1.0 GBq increase of split activity injection. There were no significant statistical differences in the rest of patient characteristics.
  
  
  CONCLUSIONS
  There is significant loss of activity observed during radioembolization, which can have a major dosimetric impact. The total administered activity and the number of split injections during radioembolization are the main influencing factors. Further prospective studies as well as measures of clinical outcome are warranted.
authors.affiliation: Department of Nuclear Medicine, Clínica Universidad de Navarra, Avenida Pio XII, 36, Pamplona, 31008, Navarra, Spain. lsanchor@unav.es.
authors.forename: Lidia Sancho
authors.identifier: http://orcid.org/0000-0002-1666-072X
authors.initials: LS
authors.lastname: Rodríguez
authors.affiliation: Department of Nuclear Medicine and PET, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore.
authors.forename: Sue Ping
authors.initials: SP
authors.lastname: Thang
authors.affiliation: Division of Research, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore.
authors.forename: HuiHua
authors.initials: H
authors.lastname: Li
authors.affiliation: Department of Diagnostic Imaging, National University Hospital, Singapore, 5 Lower Kent Ridge Rd, Singapore, 119074, Singapore.
authors.forename: Lih Kin
authors.initials: LK
authors.lastname: Khor
authors.affiliation: Department of Nuclear Medicine and PET, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore.
authors.forename: Young Soon
authors.initials: YS
authors.lastname: Tay
authors.affiliation: Department of Nuclear Medicine and PET, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore.
authors.forename: Khin Ohnmar
authors.initials: KO
authors.lastname: Myint
authors.affiliation: Department of Nuclear Medicine and PET, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore.
authors.forename: Aaron Kian Ti
authors.initials: AK
authors.lastname: Tong
mesh_terms: D000368:Aged; D004621:Embolization, Therapeutic / Q000379:methods*; D005260:Female; D006801:Humans; D008113:Liver Neoplasms / Q000473:pathology / Q000628:therapy*; D008297:Male; D008863:Microspheres; D008875:Middle Aged; D011874:Radiometry; D012117:Resins, Synthetic / Q000737:chemistry*; D012189:Retrospective Studies; D015021:Yttrium Radioisotopes / Q000737:chemistry* / Q000627:therapeutic use*
chemical_list: D012117:Resins, Synthetic; D015021:Yttrium Radioisotopes
keywords: Liver neoplasms; Radiation dosimetry; Radioembolization; Remnant activity; Yttrium-90