ENDOCRINOLOGY - I
Diagnostic procedures 

The Quarterly Journal of Nuclear Medicine 1999 September;43(3):188-94

Copyright © 2000 EDIZIONI MINERVA MEDICA

lingua: Inglese

131I whole body scintigraphy in thyroid cancer patients

Lind P.

From the Department of Nuclear Medicine and Endocrinology, PET Center LKH Klagenfurt, Austria

Iodine-131 is the ­most spe­cific radio­nu­clide to ­follow up ­patients ­with dif­fer­en­tiated thy­roid ­cancer (DTC). How­ever ­there are ­some ­aspects ­that ­should be con­sid­ered if 131I ­whole ­body scin­tig­raphy (131I WBS) is per­formed. 1) Sev­eral ­prior con­di­tions, ­including a ­bTSH ­above 30 mU/l and an uri­nary ­iodine excre­tion ­below 100-150 μg/g ­Crea, ­should be ful­filled. 2) ­Only ­about two ­thirds of metas­tases ­from DTC accu­mu­late ­iodine. There­fore, in addi­tion to 131I WBS, ­there is a ­need for ­other non­spe­cific ­tracers ­such as 99mTc Tet­ro­fosmin WBS, 99mTc Ses­ta­mibi WBS or F-18 FDG PET to ­detect ­also ­iodine neg­a­tive recur­rences or metas­tases. ­These new ­tracers, espe­cially F-18 FDG PET ­have dem­on­strated a ­very ­high detec­tion ­rate of ­iodine neg­a­tive metas­tases ­with ­mostly low dif­fe­ren­ti­a­tion. 3) The sen­si­tivity of 131I WBS ­depends on the admin­is­tered ­dose. ­Whereas the sen­si­tivity of a diag­nostic 131I WBS (up to 185 MBq) is ­below 60%, the ­value for a ­post-ther­a­peutic 131I WBS (­after 3700-7400 MBq) ­increases up to 75%. ­This ­means ­that in ­case of ele­vated ­serum thy­ro­glob­ulin, ­iodine pos­i­tive metas­tases ­cannot be ­excluded ­until WBS ­after 131I ­therapy is per­formed. 4) In ­patients ­with ele­vated ­serum thy­ro­glob­ulin and/or ­known metas­tases, who are sched­uled for 131I treat­ment, the ques­tion ­arises ­whether a diag­nostic 131I WBS ­should be per­formed and if so, ­which ­dose ­should be admin­is­tered to ­avoid thy­roid stun­ning. ­There is evi­dence in the lit­er­a­ture ­that the ­dose for a pre-ther­a­peutic diag­nostic 131I WBS ­should not ­exceed 74 MBq. 5) ­Despite the ­high spec­i­ficity of 131I WBS, sev­eral pit­falls of ­iodine accu­mu­la­tion in non-malig­nant dis­eases and malig­nan­cies of ­other ­origin ­than thy­roid ­cancer ­should be ­taken ­into ­account.