Comparison between remnant and red-marrow absorbed dose in thyroid cancer patients submitted to 131I ablative therapy after rh-TSH stimulation versus hypothyroidism induced by L-thyroxine withdrawal.
OBJECTIVE
In thyroidectomized patients, increased levels of thyroid stimulating hormone (TSH) are necessary to maximize I uptake. Traditionally, this has been achieved by withdrawing L-thyroxine (L-T4) for 4-6 weeks, inducing hypothyroidism in patients. The availability of a genetically engineered version of the recombinant human TSH (rh-TSH) provides an alternative tool to enhance the TSH serum level without inducing hypothyroidism. In this paper the I remnant and red-marrow doses calculated in differentiated thyroid cancer (DTC) patients pre-treated with rh-TSH are compared to those calculated in patients in hypothyroidism induced by L-T4 withdrawal.


METHODS
Forty-six DTC patients, submitted to I ablative therapy, were randomly divided in group A (pre-treated with rh-TSH) and group B (treated after L-T4 withdrawal for 30 days). The red-marrow absorbed dose per unit administered activity and the remnant cumulated activity per unit administered activity were calculated for both groups.


RESULTS
The red-marrow dose in 17 rh-TSH treated patients is 0.06+/-0.02 mGy.MBq; that in 14 hypothyroid patients is 0.09+/-0.03 mGy.MBq (two-tailed unpaired t-test P=0.003). The remnant cumulated activity per unit administered activity in 10 rh-TSH treated patients is 0.9+/-0.8 h; that calculated in 21 hypothyroid patients is 1.55+/-1.05 h (two-tailed unpaired t-test P=0.063). This last result is mainly due to the difference between the maximum uptake (U) in rh-TSH (U=0.01+/-0.01) and hypothyroid patients (U=0.03+/-0.02) (two-tailed unpaired t-test P=0.019).


CONCLUSIONS
The rh-TSH pre-treated patients seem to have a lower uptake compared to those in hypothyroidism induced by L-T4 withdrawal. On the other hand their red-marrow absorbed dose seems to be lower.
Vaiano
Angela
A
U.O. Fisica Sanitaria, Azienda Ospedaliero-Universitaria Pisana, Azienda Ospedaliero-Universitaria Pisana ed Università di Pisa, Italy.
Claudio Traino
A
A
Boni
Giuseppe
G
Grosso
Mariano
M
Lazzeri
Patrizia
P
Colato
Chiara
C
Davì
Maria Vittoria
MV
Francia
Giorgio
G
Lazzeri
Mauro
M
Mariani
Giuliano
G
Ferdeghini
Marco
M
D000328:Adult; D000368:Aged; D001853:Bone Marrow / Q000000981:diagnostic imaging* / Q000378:metabolism*; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000000981:diagnostic imaging* / Q000209:etiology; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D011874:Radiometry; D011877:Radionuclide Imaging; D011994:Recombinant Proteins / Q000627:therapeutic use; D013375:Substance Withdrawal Syndrome / Q000000981:diagnostic imaging*; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D013965:Thyroidectomy; D013972:Thyrotropin / Q000627:therapeutic use*; D013974:Thyroxine / Q000009:adverse effects* / Q000627:therapeutic use
D007457:Iodine Radioisotopes; D011994:Recombinant Proteins; D013972:Thyrotropin; D013974:Thyroxine