title: Pharmacokinetics and dosimetry of iodine-125-IUdR in the treatment of colorectal cancer metastatic to liver.
abstract: The radiotoxicity of 125I is highly sensitive to the site of decay relative to nuclear DNA. This paper describes a new approach, based upon pharmacokinetic clearance of radioactivity from the tumor, with which to quantify the fraction of [125I]IUdR incorporated within the DNA of tumor cells.
  
  
  METHODS
  Patients were injected with [125I]IUdR through the hepatic artery. Iodine-131-IUdR was used as a tracer for imaging and quantitation. Both conventional and DNA-level dosimetry were performed.
  
  
  RESULTS
  We calculated that if 15% of the tumor cells were in S phase at the time of injection, there would be 250 decays of 125I in the DNA per tumor cell after an infusion of 5 mCi [125I]IUdR. According to in vitro data based on 5 x 10(8) cells per g tumor, 99% of these cells in S phase would be killed.
  
  
  CONCLUSIONS
  The estimate of cell inactivation is strongly dependent on the number of cells per gram and the fraction of cells in S phase at the time of injection, which indicates that repeat injections would be necessary to achieve a therapeutic effect.
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
authors.forename: F
authors.initials: F
authors.lastname: Daghighian
authors.forename: J L
authors.initials: JL
authors.lastname: Humm
authors.forename: H A
authors.initials: HA
authors.lastname: Macapinlac
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.forename: J
authors.initials: J
authors.lastname: Izzo
authors.forename: R
authors.initials: R
authors.lastname: Finn
authors.forename: N
authors.initials: N
authors.lastname: Kemeny
authors.forename: S M
authors.initials: SM
authors.lastname: Larson
mesh_terms: D001853:Bone Marrow / Q000528:radiation effects; D015179:Colorectal Neoplasms / Q000473:pathology*; D006499:Hepatic Artery; D006801:Humans; D007065:Idoxuridine / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*; D007269:Injections, Intra-Arterial; D007457:Iodine Radioisotopes / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*; D008099:Liver / Q000000981:diagnostic imaging; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000556:secondary*; D011874:Radiometry; D011877:Radionuclide Imaging; D011879:Radiotherapy Dosage
chemical_list: D007457:Iodine Radioisotopes; D007065:Idoxuridine