Pharmacokinetics and dosimetry of iodine-125-IUdR in the treatment of colorectal cancer metastatic to liver.
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.
Daghighian
F
F
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Humm
J L
JL
Macapinlac
H A
HA
Zhang
J
J
Izzo
J
J
Finn
R
R
Kemeny
N
N
Larson
S M
SM
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
D007457:Iodine Radioisotopes; D007065:Idoxuridine