Reply: Differentiated Thyroid Carcinoma: Is There Any Evidence for the Use of Recombinant Human TSH in Thyroid Hormone–Secreting Metastasis?

REPLY: I would like to thank Schneider et al. for their compliments regarding our article (1), and I value and appreciate their time in submitting their concerns regarding our recommendations at the end of the article.

For the reader, the correct quotation of our recommendation from our article was “the use of rhTSH is appropriate for patients who cannot…increase their endogenous TSH because their metastases are producing significant thyroid hormone.” As Schneider et al. point out correctly, our article does not address the appropriate or inappropriate use of recombinant human thyroid-stimulating hormone (rhTSH) in those rare patients with differentiation thyroid cancer whose endogenous thyroid-stimulating hormone (TSH) cannot be increased because their metastases are producing a significant amount of thyroid hormone. In retrospect, I believe that I could have chosen a better phrase to have communicated my original intent in that “the use of rhTSH injections is still appropriate to consider in patients who cannot increase their endogenous TSH because their metastases are producing significant thyroid hormone.” Again, I appreciate the time and effort of Dr. Schneider et al. in bringing this to the readers’ and my attention.

Having said that, I believe an even more important point is noted by Schneider et al. in their original case report, in which they emphasize that “even standard activities of 7.4 GBq (200 mCi) [of] ¹³¹I may constitute a crucial dose in the rare combination of thyroid hormone secreting metastases and rhTSH-stimulation….(2)” And as they further state, “higher standard [fixed] activities of ¹³¹I should not be used without pretherapeutic dosimetry in patients with such large functioning metastases.” I certainly agree with and support this comment. In addition, I believe that pretherapeutic dosimetry should not just be performed in a patient, like theirs, who is being considered for a fixed prescribed activity higher than 7.4 GBq (200 mCi), but pretherapeutic scans and pretherapeutic dosimetry should also be performed in all patients who are being considered for ¹³¹I therapy and have documented or suspected functioning metastatic differentiated thyroid cancer. As has been reported by multiple authors, including Leeper (3), Tuttle et al. (4), and Kulkarni el al. (5), as many as approximately 10%–20% of patients may receive over 200 cGy (rad) to the blood (e.g., bone marrow) if prescribed activities of ¹³¹I ranging from 3.7 GBq (100 mCi) to 7.4 GBq (200 mCi) are administered. (Additional restrictions apply, including not administering a prescribed activity of ¹³¹I that would result in more than 4.44 GBq [120 mCi] of ¹³¹I whole-body retention at 48 h in patients without pulmonary metastases and 2.96 GBq [80 mCi] of ¹³¹I whole-body retention at 48 h in patients with pulmonary metastases.) In fact, as reported by Schneider et al. and using the OLINDA/EXM software, they calculated that the patient’s blood-absorbed dose was 320 cGy (rad). If full dosimetry is not available, then the use of one of the simplified dosimetric alternatives such as percentage 48-h whole-body retention as proposed by Hänscheid et al. (6) or Van Nostrand et al. (7) should be considered in order to identify those patients whose prescribed activity of ¹³¹I should be reduced. These simplified methods can be performed in almost any nuclear medicine facility.

Again, I thank Schneider et al. for their compliments, comments, and time.

• © 2012 by the Society of Nuclear Medicine and Molecular Imaging, Inc.