The relationship between Star-shaped Intense uptake of¹³¹I on whole body scan and ablation efficacy and recurrence rate for differentiated thyroid carcinoma

Objectives: After initial radioactive iodine(RAI) treatment for differentiated thyroid carcinoma(DTC) patients, we sometimes find a star-shaped intense uptake of ¹³¹I on therapeutic doses whole body scans(WBS), called star artifact. At present,there is no specific conclusion about star-shaped intense uptake of ¹³¹I. We analyzed the relevant factors and clinical implications of star artifact on the ablation efficacy and recurrence rate of DTC patients.

Methods: From January 2013 to December 2014, total 809 patients who received ¹³¹I dose of 30-150mci for the initial treatment and who did not show distant metastasis at the time of diagnosis were retrospectively evaluated. We evaluated the ablation efficacy with the American Thyroid Association(ATA) guidelines released in 2015 after six months at the initial RAI treatment and analyzed the recurrence rate of DTC patients. Ablation efficacy was divided as excellent response(ER), biochemical incomplete response(BIR), indeterminate response(IR), and structural incomplete response(SIR). Among them, 386 patients(47.7%) showed a star artifact.

Results: In the group with star artifacts, the patients were younger(P=0.003), and had a lower proportion of female(64.2% vs 80.4%,P=0.000), thyroid peroxidase antibody(TPOAb) and anti-thyroglobulin(TgAb) positive rate (9% vs 15.6%,P=0.003), thyroid static imaging negative(14% vs 57.7%,P=0.000). There was no significant difference in the success rate between patients with and without star artifact, as defined by negative 5mci diagnostic dose WBS after six months at the initial RAI treatment. In patients with first stimulated thyroglobulin(sTg) levels>10ng/ml, patients with star artifacts had a higher rate of ER compared with those without star artifact(31.6% vs 13.1%,P=0.008) and had a similar rate of BIR, IR,SIR(30.7% vs 37.8%, 21.8% vs 27.9%, 15.8% vs 21.3% respectively) . When sTg is below 10ng/ml, there was no significant difference in the ER,BIR,IR,SIR rate with and without star artifact(76.1% vs 73%, 0.79% vs 0.34%, 22.7% vs 26%, 0.4% vs 0.66% respectively). The 4 0r 5- year recurrence rate was significant difference (4.6% vs 2.8%, P=0.000) with and without star artifact.

Conclusions: Star artifacts at initial RAI treatment hint a higher ER rate when sTg levels>10ng/ml. However, star artifacts also imply a higher recurrence rate compared with those without star artifact.

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