Low dose radioiodine therapy: A review of dosimetry and evaluation of potential shielding materials for neck collars

Radioactive iodine (131I) has become the most widely used treatment for patients with thyroid cancer in Sri Lanka. This study aims to measure the radiation dose rate emitted from the 131I treated patients as outpatient basis at the Nuclear Medicine Unit (NMU), University of Peradeniya, Sri Lanka and synthesize a lead-free material to be used as a shielding collar to minimize the radiation exposure to the family members and the general public. Routinely, an average activity of 1110 MBq (30 mCi) is administered orally to thyroid cancer patients following a thyroidectomy. A total number of 40 patients including 7 men and 33 women were monitored for radiation dose rate after administering the radioiodine. The dose rate was measured after 1 hour of 131I administration at 1.0 m distance from the patient’s neck. The results showed moderately high dose rates from these patients when compared to permissible dose rates to the general public in other countries. Hence, measures should be taken to reduce the dose rates at the releasing time of the patients. Four types of shielding materials were synthesized to make a collar. The best shielding material identified was iodine incorporated silicon-based rubber with a reduction percentage of 38.48%.