Diurnal variations in biodistribution of the radionuclide I-131 in mice

• Background: Radionuclides are routinely used to diagnose and treat many different types of cancer. I-131 is a well-established radioisotope used in e.g. treatment of thyroid cancer and neuroblastoma. Accurate knowledge of I-131 biodistribution is essential to correctly estimate the absorbed dose to normal organs and determine potential risks from I-131 exposure, which is especially important when treating children. Many biological functions in living organisms follow a circadian rhythm. Nevertheless, little is known about diurnal variations in radionuclide biodistribution. This study investigates if circadian rhythm affects I-131 biodistribution in mice and absorbed dose to organs and tissues. Materials & Methods: The radioactivity concentration in mice tissues was studied at different time-points after administration of I-131, and absorbed doses were calculated. The effect of circadian rhythm was studied by varying the time of administration. Results: Difference in activity concentration between the administration time-points was observed at many time-points after administration for most investigated tissues. For some organs differences were also observed in the absorbed dose. The highest activity concentration and absorbed dose were found in the thyroid regardless of time of administration. Conclusion: The results demonstrate that the biodistribution of I-131 in mice is influenced by the time of day of administration. These findings advocate that circadian rhythm should be considered in biodistribution studies and suggests that time-point of administration of radiopharmaceuticals containing I-131 for therapy can be further optimized. An optimized time-point could result in higher absorbed dose to the tumor and/or lower absorbed dose to normal tissues.

Subject headings

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Radiologi och bildbehandling (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Radiology, Nuclear Medicine and Medical Imaging (hsv//eng)

Keyword

Biodistribution

I-131

circadian rhythm

thyroid

mouse

dosimetry

Publication and Content Type

vet (subject category)

kon (subject category)