In this week's BMJ Gangopadhyay and colleagues report the case of an unfortunate patient who activated an airport radiation detector six weeks after receiving radioiodine ¹³¹I therapy and was consequently subjected to intense examination and interrogation (p 293).1 No clinical practice guidelines cover this type of problem. So, on current evidence, how should doctors advise patients who are about to receive radioiodine therapy?

Each year radioiodine is administered to 10 000 people for hyperthyroidism in the UK.2 After injection or ingestion, radioiodine initially concentrates in the thyroid gland and then circulates through the bloodstream, with 80% excreted renally. While the radioactive urine is stored in the bladder, until it is voided, the gonads are irradiated: after an administered dose of 750 MBq …