Endocrine Abstracts (2006) 11 P916

Radioiodine treatment for hyperthyroidism – do royal college guidelines suggest too high a radioiodine dose?

R Zakir Ahmed1 & JP Hosker2

1Northern General Hospital, Sheffield, United Kingdom; 2Doncaster Royal Infirmary, Doncaster, United Kingdom.

Radioiodine (RAI) has been used to treat hyperthyroidism for more than 60 years. However there is no absolute clarity in the appropriate dose or method of administering RAI. We evaluated the efficacy of RAI therapy and compared our RAI doses with the guide doses suggested by Royal College of Physicians (Graves’ disease 400–550 MBq and Multinodular goitre (MNTG) >550 MBq).

We audited 602 hyperthyroid patients treated with RAI between 1994–2004. They were etiologically classified into Graves’ disease, MNTG and unspecified diagnosis. Although our patients received 120 Seiverts or 140 Seiverts of RAI using dosimetry, they received a wide range of absolute radiation doses. After RAI therapy patients were categorised as hypothyroid, euthyroid and relapsed hyperthyroidism.

41% of patients had Graves’, 13.6% had MNTG and rest had unspecified diagnosis. Overall cure rate was 86% with a median RAI dose of 333 MBq (241–456).There was no significant difference in cure rates between.Graves’ and MNTG patients (90% vs 82%; p not significant). The median dose of RAI for Graves’ was lower than MNTG (332 vs 419 MBq, P<0.0002).

Interestingly patients with Graves’ disease had a higher cure rate with <400 MBq RAI dose compared with >550 MBq (93.1% vs 68%, P<0.005) and higher cure with 400–550 MBq than >550 MBq (90.5% vs 68%, P<0.05). Similarly patients with MNTG had a higher cure rate with <400 MBq RAI dose compared with >550 MBq (97% vs 69.6%, P<0.02) and higher cure with <400 MBq than 400–550 MBq (97% vs 66.7%, P<0.02).

Using low dose of radioiodine (<400 MBq) it is possible to achieve high cure rates for hyperthyroidism. There was no significant benefit in treating Graves’disease and MNTG with more than 400 MBq dose of radioiodine. Royal College of Physicians guidelines may suggest too high a dose of radioiodine.

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