Usefulness of 123I-spect/ct to assess the response to initial therapy in differentiated thyroid cancer patients

Abstract

The response to initial therapy of differentiated thyroid cancer (DTC) is recommended to be evaluated 6–12 months after treatment via basal and/or stimulated-thyroglobulin (Tg) measurements and neck ultrasonography (nUS) [1]. Furthermore, diagnostic radioiodine whole body scintigraphy (Dx-WBS) is recommended only in selected cases [i.e., high risk DTC; positive anti-thyroglobulin antibody (TgAb), etc.] [1]. However, nUS is operator-dependent, limited in exploring the central cervical area and inherently unable to provide information concerning distant spread [2]. Accordingly, in case of undetected recurrences, an increased Tg level compounded with falsely negative nUS will be erroneously rated as intermediate or incomplete biochemical response with attached consequences in patients’ management. In order to give further insight, we retrospectively reviewed the records of 268 low to intermediate risk patients (F= 207, M= 61, female to male ratio = 3.4:1, mean age = 48.9 ± 14.7, median age = 48 years, range = 18–83) with histologically confirmed DTC [pT1-T3, Nx (0/ 1), Mx] referred to our centers since January 1st, 2017 to December 31th, 2019). Excluding patients with positive TgAb (n= 25), poorly DTC (n= 1) and age <18 years (n= 1), we considered for the present analysis a total of 241 patients affected by papillary (n= 224) or follicular (n= 17) thyroid carcinoma (PTC or FTC, respectively). All patients underwent recombinant-human-TSH (rhTSH)-aided radioactive iodine therapy (RaIT) with ablative (1.1–2.2 GBq I) or adjuvant (2.2–5.5 GBq I) activity. A post-therapy whole body scintigraphy (pT-WBS) plus SPECT/CT was obtained 5–7 days after RaIT, as previously described [3, 4]. Persistent/recurrent disease was found in 43/241 (17.8%) patients. Among them, 42 carried cervical lymph node metastases (level VI, n= 36; levels II–V, n= 4, level VI+ II–V, n= 2) and one patient carried both lymph node and lung metastasis. The response to treatment was assessed at 8–12 months by Tg levels measurement (basal and rhTSH-stimulated) and nUS, according to 2015 ATA criteria [1]. Additional I-DxWBS was performed in 51 (16.1%) patients due to additional risk factors [i.e., aggressive DTC variants (n= 15), isthmus location of primary DTC focus (n= 11), large remnants and/or extra-thyroid uptake area at pT-WBS (n= 25)]. Additional SPECT/CT acquisition was performed in case of equivocal findings after initial/on site review of the attending nuclear medicine specialists. [5, 6]. An excellent response was achieved in 225/241 (93.4%) DTC patients, including 27 (12%) who had extra-thyroid uptake at pT-WBS. Among remaining patients (n= 16), 8 (50%) had indeterminate (mean sTg: 4.5 ± 2.7 ng/ml, median = 3.85, range: 1.6–8.6) and 6/16 (37.5%) had incomplete biochemical response (mean sTg: 13.5 ± 1.0 ng/ml, median = 13.8, range 11.3–14.6). Finally, two patients (12.5%) had incomplete structural response (lymph-node metastases at IV and III Robbins’ levels, respectively), confirmed by fine-needle Tg measurement and treated surgically. * Alfredo Campennì [email protected]