Effect of previous administration of propyl-thiouracil on thyroid distribution of radioiodine. Contribution of secondary ion mass spectrometry microscopy to microdosimetry

Radiation dose delivered to thyroid gland after radioiodine treatment for Graves' disease is modified by administration of propyl-thiouracil (PTU) which decreases the radioactive iodine uptake and increases its distribution heterogeneity within the thyroid follicle. Using secondary ion mass spectrometry (SIMS) microscopy which is able to map quantitatively chemical elements on histological specimen, we measured stable (127 I) and radioactive (129 I) iodine concentration within thyroid follicles of mice. Furthermore, we estimated the size of thyroid follicles and their spacing using image analysis processing. We demonstrated that only SIMS parameters were determinant for microdosimetry in the three experimental groups studied: treated with radioiodine or PTU therapy (A) or after short disrupting (B) and control (C). It is for the group B that the therapeutic conditions are best. Our results underline the interest of SIMS for revisiting dosimetry in metabolic radiotherapy. (authors). 21 refs., 2 tabs., 2 figs