Abstract
The retained activity and Effective half life at 24h of therapeutic 131I in patients with Differentiated Thyroid Cancer (DTC) after total and non-total (sub-total, near-total, partial thyroidectomy and lobectomy) thyroidectomy were compared for patients in these 2 surgical groups. A total of 82 patients (61 females and 21 males) mean age 37.2 ± 9.3 years, mean weight 70 ± 15.6 Kg were considered in this study. 58 patients (70.73%) had papillary Cancer and 24 (29.27%) had follicular cancer. Out of 82 patients, 37 had total thyroidectomy while 45 had non total thyroidectomy (sub-total-29, near total- 10, partial thyroidectomy-4 and lobectomy- 2). 6 patients (7.3%) had metastases. The retained 131I activity (as a percentage of the administered dose in MBq) was 4.61% - 44.56% for patients with total thyroidectomy (mean-26.91 ± 12.57%) compared to 10.18% - 55.36% for patients with non-total thyroidectomy (mean-32.41 ± 12.57%). (p < 0.05) The effective half life ranged between 0.20 – 0.86 days for patients with total thyroidectomy (mean- 0.51 ± 0.21 days) and 0.20 – 1.17 days for patients with non-total thyroidectomy (mean- 0.62 ± 0.27 days). There is no significant difference in the mean effective half lives for the two groups of patients (p = 0.032). Our data suggests that exposure to radiation after ingestion of 131I is similar in both groups studied.
Highlights
Thyroid carcinomas account for approximately 1% of all human cancers [1,2] with the incidence of Differentiated Thyroid Carcinoma (DTC) varying from 2 – 10 per 100,000 [3,4] but having a high prevalence due to good prognosis [5]
It is reported that the survival rates of patients with DTC could be as high as 90% [6] due to effective therapy consisting of total thyroidectomy and radioiodine ablation
High thyroid stimulating hormone (TSH) level is used to stimulate both normal thyroid tissue and DTC to increase its uptake of 131I and to stimulate the secretion of thyroglobulin (Tg) [9]
Summary
Thyroid carcinomas account for approximately 1% of all human cancers [1,2] with the incidence of Differentiated Thyroid Carcinoma (DTC) varying from 2 – 10 per 100,000 [3,4] but having a high prevalence due to good prognosis [5]. It is reported that the survival rates of patients with DTC could be as high as 90% [6] due to effective therapy consisting of total thyroidectomy and radioiodine ablation. Treatment of patients with combination of total thyroidectomy, 131I ablation and thyroid hormone suppression result in a lower recurrence rate than surgery alone or surgery plus external radiotherapy or surgery plus thyroid hormone [7]. Iodine-131 destroys any remaining normal thyroid tissue and occult microscopic carcinomas thereby decreasing the risk of recurrence [8]. This benefit of radioiodine ablation of thyroid tissues can be fully achieved if the thyroid tissues take up a great percentage of the radioiodine that is administered. The effectiveness of Radioiodine therapy (RAI) depends on the patient’s serum TSH being sufficiently elevated to about ≥ 30mU/L which is believed to increase NIS (sodium iodide symporter) expression and thereby to optimize radioiodine uptake [10]
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