Radioactive iodine (RAI) therapy, using Iodine-131 (I-131), is a common treatment for thyroid cancer and hyperthyroidism. The concern about how long this radioactive material remains on surfaces relates to minimizing exposure risk to family members and caregivers after treatment. After the radioiodine capsule is swallowed, the body excretes the unabsorbed material through fluids like urine, sweat, and saliva. Safety guidelines regarding surface contamination are based on understanding how this radioactivity diminishes.
How Iodine-131 Decays
The duration of surface contamination risk is determined by two separate rates of reduction: physical decay and biological excretion. Iodine-131 has a physical half-life of approximately 8.02 days. This is the time required for half of the radioactive atoms to naturally transform into a stable form, Xenon-131. This rate is constant whether the material is inside or outside the body.
The more significant factor in reducing contamination risk is the biological half-life, which represents how quickly the body eliminates the radioiodine through excretion. For most patients, the majority of the unabsorbed I-131 is cleared through urine within the first 48 hours following treatment. This rapid clearance means the overall effective half-life—the combined time it takes for radioactivity to be cut in half inside the body—is often just a matter of hours.
Because the patient clears the source material so quickly, the highest risk of surface contamination occurs immediately after treatment and drastically decreases over the next one to two days. When I-131 is present on a surface, only the physical half-life of 8.02 days applies to its decay. This rapid drop in available source material significantly reduces the actual surface contamination hazard shortly after the patient is released from isolation.
Identifying High-Risk Contamination Zones
Contamination occurs when radioactive bodily fluids come into contact with objects and surfaces. Since the highest concentration of I-131 is found in urine, the bathroom is the primary high-risk zone. Surfaces that are frequently touched, especially in the first few days post-treatment, present the greatest risk of transferring the material.
The toilet seat, flusher handle, and bathroom faucet handles are particularly vulnerable. Surfaces that absorb moisture, such as towels, bedding, and clothing, are easily contaminated by sweat and saliva. Objects handled often, including light switches, door knobs, remote controls, and mobile phones, can accumulate radioactive material transferred from the hands.
Saliva and nasal secretions are also sources of contamination, meaning eating utensils, drinking glasses, and tissues must be managed carefully. Any item that comes into contact with the patient’s mouth or nose poses a risk. The goal of isolation is to prevent the spread of these contaminated fluids to shared areas.
Practical Surface Safety and Cleanup Guidelines
The most effective way to reduce surface contamination risk is to allow time for the I-131 to decay and for the patient’s body to excrete the remaining material. For non-washable items, such as books or remote controls, the primary decontamination method is to set them aside for several weeks to allow physical decay. Standard household cleaning agents are sufficient for surfaces that must be cleaned. The goal is to physically remove the radioactive material, not neutralize it chemically.
In the bathroom, patients should flush the toilet two or three times after each use to ensure all radioactive urine is completely washed down. Men should sit while urinating to minimize splatter onto the seat and surrounding floor. The sink and tub should be thoroughly rinsed after use to wash away any contaminated saliva or sweat.
For laundry, all clothing, towels, and bed linens used by the patient during the isolation period should be washed separately from the rest of the household items. If possible, a separate laundry hamper should be used. Disposable items, such as paper plates, cups, and plastic utensils, should be used and then sealed in a designated trash bag for disposal, following instructions provided by the treatment facility.