Harold L. Atkins 90 7O- \ Nofal 66 60 ; J Cassidy '68 50 Burke ‘69 Present Dunn '64 a 4% HYPO THYROID 404 - 4 Study a +” 9 Green '64 ‘ 30-4 204 10 + Oo 0 T 2 v 7 4 F T 6 q T 8 T T 10 T T l2 7 7 4 T t I6 im 4 18 YEARS AFTER '*'1 TREATMENT Fig. 6-1. Cumulative incidence of hypothyroidism in study of Glennon et al. (present study) compared with previously reported data. Solid lines indicate data originally reported using the life table method; broken lines indicate data recalculated from the reported data using the life table method. Reproduced with permission from Glennon J.A. et al., Ann. Int. Med. 76:721-723, 1972. percent required more than one dose. The 10-year incidence of hypothyroidism was an acceptable 18 percent.* Less satisfactory were the results of Glennonet al.2° who observedthe results of a single dose of 3 mCi or less for up to 17 years. Although the incidence of hypothyroidism was low at | year (3.7 percent) and at 5 years (7.5 percent), there was an annual increase of 3.4 percent thereafter, equalling the rates for higher dose series (Fig. 6-1). This illustrates the necessity for long-term follow-up and suggests that the eventual cumulated incidence of hypothyroidism cannotbe reduced by low dose '*'T. There seems to be no doubtthat the incidence of hypothyroidism at 1 and 5 years can be substantially reduced by lowering the administered dose of 13'I, but probably at the price of increasing the need for retreatment and prolonging the duration of hyperthyroidism for many patients. The longer term results at 10 to 15 years or more are not yet available in many of these series, and there is the suggestion in the data of Cevallos et al. that the differences due to the different dose regimens may be less marked at that time.’®? The data of Glennon et al. indicate that the long-term follow-up does show a high rate of hypothyroidism even after low doses.'® Multiple Small Doses The advantage of using multiple small doses (less than 50 wCi/g) is that it permits observation of the response prior to retreatment and permits individuali-