Abstract
The activity of radioiodine (131I) used in adjuvant therapy for thyroid cancer ranges between 30 mCi (1.1 GBq) and 150 mCi (5.5 GBq). Dosimetry based on Marinelli's formula, taking into consideration the absorbed dose in the postoperative tumour bed (D) should systematise the determination of 131I activity. Retrospective analysis of 57 patients with differentiated thyroid cancer (DTC) after thyreidectomy and adjuvant 131I therapy with the fixed activity of 3.7 GBq. In order to calculate D from Marinelli's formula, the authors took into account, among other things, repeated dosimetry measurements (after 6, 24, and 72 h) made during scintigraphy and after administration of the therapeutic activity or radioiodine. In 75% of the patients, the values of D were > 300 Gy (i.e. above the value recommended by current guidelines). In just 16% of the patients, the obtained values fell between 250 and 300 Gy, whereas in 9% of the patients, the value of D was < 250 Gy. The therapy was successful for all the patients (stimulated Tg < 1 ng/ml and 131I uptake < 0.1% in the thyroid bed in follow-up examination). Dosimetry during adjuvant 131I therapy makes it possible to diversify the therapeutic activities of 131I in order to obtain a uniform value of D.
Highlights
The activity of radioiodine (131I) used in adjuvant therapy for thyroid cancer ranges between 30 mCi (1.1 GBq) and 150 mCi (5.5 GBq)
Radioiodine is administered after thyroidectomy to patients with differentiated thyroid cancer as adjuvant therapy whenever there are indications of subclinical micrometastatic disease.In other words, apart from the fact that this treatment is aimed at ablating remnant thyroid after total thyroidectomy, it is designed to destroy all the cancer microfoci that may have remained in the thyroid bed and local lymph nodes
In view of the above, the purpose of this paper is to prove, by using dosimetric methods during whole-body scintigraphy after administration of fixed 131I activity, that it is justified to diversify the therapeutic activity of 131I in order to obtain a uniform absorbed dose in each case
Summary
The activity of radioiodine (131I) used in adjuvant therapy for thyroid cancer ranges between 30 mCi (1.1 GBq) and 150 mCi (5.5 GBq). Radioiodine is administered after thyroidectomy to patients with differentiated thyroid cancer as adjuvant therapy whenever there are indications of subclinical micrometastatic disease (microscopic invasion of perithyroid soft tissue, histologically aggressive cancer, i.e. tall cell, insular, columnar cell carcinoma, Hürthle cell carcinoma, follicular thyroid cancer, or hobnail variant, vessel-invading tumor, clinical N1, Brafv600E mutated multifocal papillary microcarcinoma).In other words, apart from the fact that this treatment is aimed at ablating remnant thyroid after total thyroidectomy, it is designed to destroy all the cancer microfoci that may have remained in the thyroid bed and local lymph nodes As a consequence it leads to improving disease-specific survival, decreasing recurrence rates, as well as improving progression-free s urvival[1,2,3,4]. Radiation therapy include elevated risk of secondary carcinomas, e.g. leukaemia (so-called stochastic effects), temporary lower fertility and impaired function of the testes (so-called deterministic effects)[9,10,11,12]
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