Post-surgical ablation of thyroid remnants with high-dose 131I in patients with differentiated thyroid carcinoma

Abstract

The aims of this study were to evaluate the efficacy of an empirically determined "fixed" high ablative dose of radioiodine ((131)I) therapy and to determine the utility of ultrasonography (US) in dose determination. A retrospective analysis was performed of 242 thyroid cancer cases treated with "fixed" high-dose (131)I for ablation of thyroid remnants without a pre-ablative (131)I diagnostic scintigraphy or radioiodine uptake study. Treatment doses ranged from 1850 MBq (50 mCi) to 7.4 GBq (200 mCi). The selection of the treatment dose was based on the surgical and pathological findings as well as the remnant thyroid volume calculated by US. A successful ablation was defined as the absence of activity in the thyroid bed on subsequent imaging studies. Successful ablation was obtained in 218 of the 242 patients (90%). In 162 of the 218 patients (74.3%), successful ablation was achieved after a single (131)I treatment. The remnant thyroid volume calculated by US was significantly different (P=0.04) between those who were successfully ablated and those who were not. The total (131)I dose needed for successful ablation was significantly higher in males (P=0.003). Patients with higher post-operative thyroglobulin (Tgb) levels and patients with a higher stage of disease required higher doses (P=0.036 and P=0.021 respectively). Serum Tgb levels were under 10 ng.ml(-1) in 220 of the 242 patients (90%) following radioiodine ablation while not receiving L-thyroxine suppression. Nineteen patients (7.8%) showed metastases on post-therapy scan and successful treatment was achieved in 11 of 19 (57.8%). Four of the 19 patients with distant metastases (revealed on post-treatment scan) were found to have been given a treatment dose of less than 200 mCi based on the proposed empirical approach. These results indicate that "fixed" high-dose (131)I treatment is clinically feasible with an acceptable dose underestimation rate, and the utilization of US in the determination of the thyroid remnant volume provides more accurate and reproducible results.

Thyroid nodules and differentiated thyroid cancer: update on the Brazilian consensus

“…For that purpose, neck US is superior to scintigraphy and also provides information on the persistence of lymph node metastases (89,90). For this purpose, a 3-month interval is required between surgery and ultrasonographic assessment (90).…”

Thyroid remnant volume and Radioiodine ablation in Differentiated thyroid carcinoma

“…Thyroid remnant volume is one of the predictor of complete ablation (8,9). There are several ways to determine thyroid remnant volume (6).…”

“…Successful ablation depends on type of surgery, thyroid remnant volume, radioactive iodine uptake (RAIU), effective half-life (EHF) of I-131 etc (5,6). There are several studies on thyroid remnant volume and radioiodine ablation (7,8,9). Thyroid remnant can be assessed clinically or by surgeon's notes or by imaging such as ultrasonography or scintigraphy (6).…”

Maximal safe dose of I-131 after failure of standard fixed dose therapy in patients with differentiated thyroid carcinoma

“…In this sense, MSD appears to be the more effi cient dosimetric method in clinical practice. However, few investigators have reported results of the MSD method [8][9][10] after it was initially proposed by Benua et al [6]. In particular, no trial of the MSD method has been conducted in patients with residual thyroid cancer who have failed conventional fi xed dose I-131 therapy.…”