Abstract
There is controversy about ablation efficacy of low or high doses of radioiodine-131 (RAI) in patients with differentiated thyroid cancers (DTC). The purpose of this prospective study was to determine efficacy of 30 mCi and 100 mCi of RAI to achieve successful ablation in patients with low to intermediate risk DTC. This prospective cross sectional study was conducted from April 2013 to November 2015. Inclusion criteria were patients of either gender, 18 years or older, having low to intermediate risk papillary and follicular thyroid cancers with T1-3, N0/N1/Nx but no evidence of distant metastasis.Thirty-nine patients were administered 30 mCi of RAI while 61 patients were given 100 mCi. Informed consent was acquired from all patients and counseling was done by nuclear physicians regarding benefits and possible side effects of RAI. After an average of 6 months (range 6-16 months; 2-3 weeks after thyroxin withdrawal), these patients were followed up for stimulated TSH, thyroglobulin (sTg) and thyroglobulin antibodies, ultrasound neck (U/S) and a diagnostic whole body iodine scan (WBIS) for ablation outcome. Successful ablation was concluded with stimulated Tg< 2ng/ml with negative antibodies, negative U/S and a negative diagnostic WBIS (triple negative criteria). ROC curve analysis was used to find diagnostic strength of baseline sTg to predict successful ablation. Successful ablation based upon triple negative criteria was 56% in the low dose and 57% in the high dose group (non-significant difference). Based on a single criterion (follow-up sTg<2 ng/ml), values were 82% and 77% (again non-significant). The ROC curve revealed that a baseline sTg level ≤ 7.4 ng/ml had the highest diagnostic strength to predict successful ablation in all patients. We conclude that 30 mCi of RAI has similar ablation success to 100 mCi dose in patients with low to intermediate risk DTC. A baseline sTg ≤ 7.4 ng/ml is a strong predictor of successful ablation in all patients. Low dose RAI is safer, more cost effective and more convenient for patients and healthcare providers.
Highlights
Differentiated thyroid cancer (DTC) is the most common endocrine malignancy comprised of papillary (80%) and follicular (10%) types and is associated with high 10-year survival rate (90 to 95%) (Sawka et al, 2004; Zaman et al, 2013)
Radioiodine-131 use as an adjuvant option is well established in high risk patients with differentiated thyroid cancer
Our study clearly shows equal ablation efficacy of 30 mCi RAI as compared to 100 mCi dose
Summary
Differentiated thyroid cancer (DTC) is the most common endocrine malignancy comprised of papillary (80%) and follicular (10%) types and is associated with high 10-year survival rate (90 to 95%) (Sawka et al, 2004; Zaman et al, 2013). In Pakistan as per local nuclear regulatory authority, a patient receiving ≥ 30 mCi of RAI needs to be admitted in isolation till radiation exposure falls down to
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