Systemic iodine 125 activity after GliaSite brachytherapy: safety considerations

After contaminated radioactive linens were detected on the completion of intracranial brachytherapy for a patient episodically incontinent of urine, the systemic absorption of iodine 125 from the GliaSite Radiation Therapy System was studied. Diffusion and leakage of (125)I through the walls of the GliaSite balloon catheter have previously been reported to be negligible in both animal and human studies examining the radioactivity of urine during and after treatment. Our study estimated total systemic absorption based on activity defect measurements rather than using urinary excretion as a surrogate.

Six patients treated with complete data were reviewed. The activity at the time of injection was compared to the activity recovered on completion of treatment after adjustment for decay.

By comparing the activity of (125)I infused with the activity recovered, 0.5-5.5% of infused (125)I remained unaccounted after adjusting for decay over the 4-day treatment period. The patient with contaminated hospital linens due to urinary incontinence had unaccounted activity of 2.3%. Comparisons of the volume of liquid (125)I and saline removed on completion to treatment to the volume originally instilled revealed no difference using hand-held syringes.

The systemic absorption of (125)I is much greater than previously appreciated with potential clinical sequelae and safety concerns. GliaSite should be used with caution in patients incontinent of urine, and a Foley catheter should be placed to collect contaminated urine for incontinent patients.