Radioiodine dispensing and usage in a centralized hospital nuclear pharmacy

Received dose variability after administration of I-131 for treatment of hyperthyroidism in cats

BACKGROUND

Injectable radioactive iodine (I-131) frequently is used to treat hyperthyroidism in cats. In human medicine, residual activity after injection of radionuclides has been reported, and the actual quantity administered is recorded after administration.

OBJECTIVE

Our aim was to evaluate actual administered dose variability after administration of preprepared I-131 single unit doses for the treatment of hyperthyroidism in cats.

ANIMALS

Twenty-seven cats with hyperthyroidism treated with I-131 between April 2017 and March 2019.

METHODS

Retrospective observational study of cats treated with preprepared single unit I-131 doses. For each dose, the measured activity before administration and residual activity were recorded. The measured dose and the actual dose administered were compared to the prescribed dose.

RESULTS

Measured activity before administration ranged from 88.4% to 103.3% of the prescribed dose. Mean residual activity was 5.2 ± 3.0 MBq (ranging from 1.5% to 15% of the prescribed dose). The actual dose administered (measured activity - residual activity) ranged from 79.1% to 100.2% of the prescribed dose. Seventeen of 28 (60.7%) of the actual administered doses differed between 10% and 20% of the prescribed dose. One administered dose had a >20% difference compared to the prescribed dose (79.10% of the prescribed dose).

CONCLUSION AND CLINICAL IMPORTANCE

Our study identified variability in the residual and actual administered activity of I-131 as compared to the prescribed dose, which should be taken into consideration when treating cats with (predrawn) I-131.

Adaptation of hard gelatin capsules for oral delivery of aqueous radiopharmaceuticals

PURPOSE

Oral administration of Iodine-131 (I-131) solutions causes high risk of contamination for patients and dispensers. The objective of the study was to adapt hard gelatin capsules (HGCs) for filling with radiopharmaceutical solutions without deformation.

METHODS

Polystyrene (PS) internally lining films with different thicknesses were used to protect HGCs. The insulated HGCs were evaluated for their physicochemical characteristics and rupturing time in different dissolution media. HGCs internally lined with PS were examined for withstand loading with different volumes and radioactivities of I-131 solutions. Radioactivity release was studied in deionized water and acidic media. Quality control of released I-131 was inspected for radiochemical purities.

RESULTS

There was a directly proportion between PS lining thickness and stability of HGCs after filling with 500 μl aqueous methylene blue solution. HGCs internally lined with PS 100 μm thickness withstand deformation for ˃ two months; however showed fast in-vitro rupturing time in different dissolution media. Internally lined HGCs loaded with different volumes and radioactivities of I-131 solutions resisted for one week without radioactive leakage. Yet, revealed complete release of I-131 after 20 min in dissolution media with great radiochemical purity.

CONCLUSION

The study promises safely I-131 aqueous solution delivery via adapted HGCs. Graphical abstract Oral administration of radiopharmaceuticals.

Thyroid uptake of liquid versus capsule 131I tracers in hyperthyroid patients treated with liquid 131I

The amount of 131I used to treat hyperthyroid patients is based in part on the 24-hour thyroid uptake of a diagnostic amount of radioiodine (tracer). We compared the 24-hour uptake of an 131I tracer administered in liquid or capsule form to the 24-hour uptake of 131I therapy administered as liquid. Sixty-five hyperthyroid patients with Graves' disease were evaluated and subsequently treated with radioiodine. The liquid group (45 patients) received a liquid 131I tracer (1.85 MBq [0.05 mCi]) and the capsule group (20 patients) received a capsule 131I tracer (1.63 MBq [0.044 mCi]). Probe calibration factors were the same for the liquid and capsule 131I standards. All patients received therapeutic amounts of 131I [114.7-1106.3 MBq [3.1-29.9 mCi]) in liquid form. Therapy uptakes were obtained using the same collimated uptake probe modified with a calibrated lead shield to attenuate the high photon flux. The mean therapeutic uptake was the same for both groups (58%). The mean diagnostic uptake for the capsule group, however, was less than the mean diagnostic uptake for the liquid group (44% vs. 63%). The mean diagnostic uptake for the capsule group was significantly lower than the mean therapeutic uptake for this group (44% vs. 58%), whereas the mean diagnostic and therapeutic uptakes were similar for the group receiving a liquid tracer (63% vs. 58%). In conclusion, diagnostic uptakes performed with a liquid tracer more accurately predicted liquid therapy uptakes than diagnostic uptakes performed with a capsule tracer. This raises concern about the bioavailability of 131I in capsule form and has implications for determining the amount of 131I to administer for therapy. Patients whose 131I therapy was based on the uptake of a capsule tracer received a higher than intended amount of radiation to the thyroid gland.