I-131 Remnant Ablation: Release, Contamination, and Instructions
A 44-year-old woman with papillary thyroid carcinoma receives 5.55 GBq (150 mCi) of 131I for remnant ablation. At 24 hours she is well, voids normally, follows instructions, and has no incontinence or confusion. Her exposure rate is 18 mR/h (180 µSv/h) at 1 m. She lives in a two-bedroom apartment with her husband and a 6-year-old son; she has her own bedroom but they share one bathroom. She works as a supermarket cashier and wants to return 3 days after therapy. Your institution applies the NRC release rule: exposure rate ≤7 mR/h at 1 m, or a calculated dose to any other person ≤5 mSv (500 mrem), with written instructions. The RSO is reachable by phone and can run a dose estimate.
1. The patient exceeds the 7 mR/h criterion. Should you keep her in the hospital until it falls below 7 mR/h? Show the reasoning.
Read the worked answer
No - waiting is not a workable strategy, and the regulation does not require it.
131I has a physical half-life of about 8.02 days (192 h). Time to fall from 18 to 7 mR/h:
- 18 → 7 is a factor of 2.57, i.e., 1.36 half-lives
- 1.36 × 192 h ≈ 261 h, or about 11 days
Holding an asymptomatic, continent, cooperative patient for 11 days for a number that barely moves day to day is not clinically or ethically sensible.
Correct pathway: use the second branch of the release rule. The RSO calculates the dose to the most exposed individual - here the 6-year-old son - using distance and occupancy factors from the actual household pattern (separate bedroom, shared bathroom, no bed sharing, no holding). If the estimate is ≤5 mSv, she is released with written instructions. If it exceeds 5 mSv, options are continued hospitalization, temporary relocation of the child, or intensified distancing until a re-estimate is acceptable.
She is continent, oriented and able to follow instructions, so she is not in the category that must be retained regardless of dose rate.
2. Outline the contamination-control plan for her room, bathroom, and personal items over the next several days.
Read the worked answer
Thyroid ablation patients excrete 131I in urine, saliva, sweat and stool, so contamination control is an ongoing process, not a one-time cleaning.
Bathroom
- She should sit to void; flush the toilet twice after each use.
- Keep her own towel and washcloth, launder separately.
- Wipe the sink and toilet with disposable pads after use; bag and hold as radioactive waste.
- Daily shower (she should not bathe with family members).
Bedroom
- Absorbent pads on the mattress; linen changed frequently, bagged, labelled and held for decay rather than sent to the general laundry.
- Separate dishes if practical, or wash separately with thorough rinsing; avoid preparing food for others.
Survey practice
- Survey the room, bathroom and personal items with a thin-window detector before the room returns to general use; mark and decontaminate hotspots; re-survey.
- Staff use gloves and check themselves for contamination after room entry.
- The husband's and son's items should not share storage with hers during the first days.
3. Draft the written instructions you would give, with specific behaviours and time frames. What do you say about her job?
Read the worked answer
Written, dated, signed, in her own language, with a contact number.
- Sleep alone for at least the next 7–11 days (use the RSO's calculated duration).
- Keep about 1 m (3 ft) of distance from her husband and especially from her son; no bed sharing, prolonged hugging, or lap sitting; brief passing contact is acceptable.
- No contact with pregnant women or young children beyond passing encounters for the same period.
- Bathroom: separate bathroom if at all possible; if not, sit to void, flush twice, clean the toilet and sink after use.
- Do not prepare food for others; wash hands frequently; shower daily.
- Laundry and utensils separate from the rest of the household; bag linen.
- Avoid public transport and long journeys for the first few days.
The job: a cashier involves prolonged close contact with the public, including potentially pregnant customers, at well under 1 m for hours. That is precisely the exposure pattern the instructions are designed to prevent. Advise not returning to work for at least 7 days, with the actual date set by the RSO's estimate. If she cannot afford to stay off work, that is a conversation for the RSO and social work, not something to resolve informally at the front desk.