Radio-iodine treatment of hyperthyroidism--a more liberal policy?
The main and most valid evidence we have is that on direct follow-up of treated patients. This has been well done in thousands of patients in two countries with very good medical care and over long periods--10 to 15 years or more. On the other hand there is no doubt about radiation carcinogenesis, and thyroid cancer has been caused in children by low-dose x-ray therapy. The possibility of other cancer and of leukaemogenesis is also real. The evidence for this is reviewed and risk estimates given. Experimental work and radiation biology is reviewed and it is suggested that the risk of thyroid cancer from the usual radio-iodine doses given for treatment is low because of cell killing or sterilization, and animal evidence is discussed that supports this. The final position appears to be that no risk has yet been demonstrated in man and evidence in general suggests that if there is indeed a cancer risk it will be less than about 0.1%. It is suggested that this is not dissimilar to surgical risks, except that these are more immediate as compared with the long latent period for development of radiation-induced cancer. Genetic risks are also discussed and again have not been demonstrated in man from this treatment and should in any case be low. The risk to children is also considered; there is no direct evidence of risk but only small numbers have been treated--nevertheless the hypothetical risk may be counterbalanced by the benefits. Administration of radio-iodine therapy to pregnant or lactating women must be scrupulously avoided; both cause significant risks. Finally, if a more liberal policy be accepted it is worth while giving optimum treatment, and evidence is given suggesting low-dose treatment similar in effect to surgical thyroidectomy and followed temporarily if need be by anti-thyroid drug treatment.