Value of postoperative thyroglobulin and ultrasonography for the indication of ablation and ¹³¹I activity in patients with thyroid cancer and low risk of recurrence.
BACKGROUND
This study investigated the value of postoperative stimulated thyroglobulin (Tg) combined with neck ultrasonography for the prediction of the posttherapy whole-body scanning (RxWBS) and the efficacy of ablation with 30 mCi ¹³¹I in patients with thyroid cancer and low risk of recurrence to identify those who do not require ablation or only need a low ¹³¹I activity.


METHODS
A total of 237 consecutive patients with well-differentiated thyroid cancer and low risk of recurrence who were initially treated by total thyroidectomy followed by remnant ablation with 1.1 or 3.7 GBq (30 or 100 mCi) ¹³¹I were studied. Neck ultrasonography, Tg after levothyroxine withdrawal, and anti-Tg antibodies (TgAb) were obtained before, and RxWBS was performed 7 days after ¹³¹I administration. Patients with TgAb were excluded.


RESULTS
Postoperative ultrasonography revealed lymph node metastases in 5/237 (2%) patients. RxWBS showed ectopic uptake in 3/232 (1.3%) patients with negative ultrasonography. The negative predictive value of postoperative stimulated Tg <1 ng/mL (n = 132) or <10 ng/mL (n = 213) combined with negative ultrasonography was 100%. Among patients with detectable postoperative stimulated Tg <10 ng/mL and negative ultrasonography, 50 received 1.1 GBq ¹³¹I and 31 received 3.7 GBq. In the control assessment, stimulated Tg <1 ng/mL and neck ultrasonography without anomalies were achieved in 47/50 (94%) and in 29/31 patients (93.5%). All patients with stimulated Tg ≤1 ng/mL, negative TgAb, and normal ultrasonography before ablation continued to show the same results 8-12 months after initial therapy as expected, irrespective of the administration of 1.1 GBq (n = 82) or 3.7 GBq ¹³¹I (n = 50).


CONCLUSIONS
Measurement of stimulated Tg combined with neck ultrasonography after total thyroidectomy may exclude the need for ablation in 56% of low-risk patients without TgAb (Tg <1 ng/mL) and permit the administration of an activity of 1.1 GBq ¹³¹I in another 34% with low Tg levels.
Postgraduation Program, Santa Casa de Belo Horizonte, Minas Gerais, Brazil. pedrorosario@globo.com
Pedro Weslley
PW
Rosario
Arthur Cezar Malard
AC
Xavier
Maria Regina
MR
Calsolari
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008207:Lymphatic Metastasis; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D011237:Predictive Value of Tests; D011877:Radionuclide Imaging; D012008:Recurrence; D012306:Risk; D013954:Thyroglobulin / Q000097:blood*; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000601:surgery; D014463:Ultrasonography / Q000379:methods*; D051598:Whole Body Imaging
D007457:Iodine Radioisotopes; D013954:Thyroglobulin