Factors Influencing the Success of the First Radioiodine Therapy for Differentiated Thyroid Carcinoma
Apichaya Claimon MD*, Pawana Pusuwan MD*, Benjapa Khiewvan MD*
Affiliation : * Division of Nuclear Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
Objective : Differentiated thyroid cancer (DTC) has a favorable prognosis following treatment by thyroidectomy and subse-
quent post-operative radioactive iodine therapy (RAIT). However, prognostic factors for the success of the first RAIT remain
inconclusive. The aim of the present study was to evaluate prognostic factors for the success of the first RAIT in DTC patients.
Material and Method: We retrospectively studied 401 DTC patients who underwent total, near-total and subtotal thyroidectomy
followed by high dose RAIT from 1994 to 2004. Successful RAIT was assessed using the following criteria: (a) stimulated
serum thyroglobulin (sTg) < 10 ng/ml; (b) negative diagnostic 131I total body scan (DxTBS); and (c) no serial increase in
thyroglobulin antibody (TgAb) levels. Factors influencing successful first RAIT were evaluated.
Results : In total, 401 patients were enrolled into the present study. Most patients were female (81.5%) and had papillary cell
type cancer (74.3%). Median tumor size was 2.55 cm. (range, 0–11 cm). Metastases at cervical node and distant sites were
found prior to RAIT in 167 and 26 patients, respectively. The first RAIT doses of 2.96–3.7, 5.5 and 7.4 GBq were administered
to 133, 262 and 6 patients, respectively. Overall success rate of the first RAIT was 32.9%. From univariate analysis, female
sex, age of <45 years, underwent thyroidectomy without cervical lymph node dissection, no multifocality, free surgical margin,
no metastasis and sTg of <20 ng/dl at ablation were prognostic factors. Age of <45 years and sTg of <20 ng/dl at ablation
were independent significant prognostic factors (both p<0.001) from multivariate analysis.
Conclusion : Age below 45 years and sTg below 20 ng/dl at ablation are independent prognostic factors for the success of
the first RAIT.
Keywords : Differentiated thyroid cancer, prognostic factors, radioiodine therapy, treatment outcome
