Protection problems in radionuclide therapy: the patient as a gamma-radiation source

Area of Science:

• Nuclear Medicine
• Radiological Physics
• Endocrinology

Background:

• Radioiodine therapy, particularly using iodine-131 (131I), is a standard treatment for hyperthyroidism and thyroid carcinoma.
• Patient administration of radioiodine results in external radiation exposure to healthcare workers and other patients.
• Accurate estimation of radiation exposure is essential for implementing effective radiation protection measures.

Purpose of the Study:

• To estimate the rate of uptake, metabolism, and excretion of radioiodine in patients undergoing therapy.
• To calculate average and variable radiation exposure levels at a given distance from patients treated with radioiodine.
• To compare potential exposures from iodine-131 (131I) therapy with those from other radioisotopes like gold-198 (198Au) and radium-226 (226Ra).

Main Methods:

• Utilized data on radioiodine uptake, metabolism, and excretion rates in patients.
• Calculated average radiation exposure at a distance of 2.5 meters (bed spacing) for typical therapeutic doses.
• Determined exposure variability based on metabolic parameter variations, estimating 90th percentile values.

Main Results:

• Mean exposure for an adjacent patient (2.5 m spacing) from 131I therapy for hyperthyroidism is estimated at 0.02 R.
• Mean exposure for an adjacent patient from 131I therapy for thyroid carcinoma is estimated at 0.08 R.
• Exposures increase to 0.03 R and 0.14 R (90th percentile) due to metabolic variations; 198Au and 226Ra treatments yield higher exposures (0.2 R and 0.6 R, respectively).

Conclusions:

• Radiation exposure from radioiodine therapy is quantifiable and depends on the administered dose and patient metabolism.
• Adjacent individuals receive low but measurable radiation doses, necessitating adherence to radiation safety guidelines.
• Iodine-131 therapy generally results in lower external radiation exposure compared to treatments with 198Au or 226Ra.