[Thyroid cancer after Chernobyl: is iodine 131 the only culprit ? Impact on clinical practice]. / Le cancer de la thyroïde après Tchernobyl: l'iode 131 seul responsable? Conséquences en termes de pratique médicale.

The large increase in the incidence of thyroid cancer among children who were mainly less than five years old at the time of the Chernobyl accident is still a major preoccupation for endocrinologists and nuclear physicians. Epidemiological studies have focused solely on iodine 131. However, past knowledge on thyroid irradiation (medical use of iodine 131, radioactive fallout on Marshall islands and the Nevada, and Hanford site releases) as well as number of recent works (about low-dose irradiation), raise question on the role of other factors. It is here shown that post-Chernobyl thyroid irradiation is complex and that all factors (iodine 131, but also short lived isotopes of iodine and external irradiation) should be considered. Finally, one need to think about some of the present medical uses of iodine 131, and especially to the treatment of hyperthyroidism in young subjects.

[Kinetics of intracolloidal iodine within the thyroid of newborn rats. Direct imagery using secondary ion mass spectrometry]. / Cinétique intracolloïdale de l'iode dans la thyroïde de rat nouveau-né. Imagerie directe par microscopie ionique analytique.

The spatiotemporal distribution of cellular uptake site of radiotoxics is essential data for microdosimetric studies. As early as 1950, the heterogeneity of iodine incorporation within the thyroid has been shown using autoradiography. The objective of this study is to describe the kinetic cellular distribution of newly organified iodine in the thyroid of newborn rats using secondary ion mass microscopy (NanoSIMS50). Ionic images obtained at high mass resolution and with a lateral resolution of about 50 nm show that the early distribution of iodine is heterogeneous from one follicle to another, from one thyrocyte to another inside the same follicle, and that this distribution varies as a function of time. The obtained kinetic profile will allow us to refine the studies concerning the aetiopathology of thyroid cancers of the Chernobyl children.

Thyroid cell irradiation by radioiodines: a new Monte Carlo electron track-structure code

The most significant impact of the Chernobyl accident is the increased incidence of thyroid cancer among children who were exposed to short-lived radioiodines and 131-iodine. In order to accurately estimate the radiation dose provided by these radioiodines, it is necessary to know where iodine is incorporated. To do that, the distribution at the cellular level of newly organified iodine in the immature rat thyroid was performed using secondary ion mass microscopy (NanoSIMS50). Actual dosimetric models take only into account the averaged energy and range of beta particles of the radio-elements and may, therefore, imperfectly describe the real distribution of dose deposit at the microscopic level around the point sources. Our approach is radically different since based on a track-structure Monte Carlo code allowing following-up of electrons down to low energies (~ 10eV) what permits a nanometric description of the irradiation physics. The numerical simulations were then performed by modelling the complete disintegrations of the short-lived iodine isotopes as well as of 131I in new born rat thyroids in order to take into account accurate histological and biological data for the thyroid gland.

O impacto mais significante do acidente de Chernobyl é o crescimento da incidência de câncer de tireóide em crianças que foram expostas a radioiodos de vida curta e ao Iodo-131. Na estimativa precisa da dose de radiação fornecida por esses radioiodos, é necessário conhecer onde o iodo está incorporado. Para obtermos esse resultado, a distribuição em nível celular de iodo recentemente organificado na tireóde de ratos imaturos foi realizada usando microscopia de massa iônica secundária (NanoSIMS50). Modelos dosimétricos atuais consideram apenas a energia média das partículas beta dos radioelementos e pode, imperfeitamente descrever a distribuição real de dose ao nível microscópico em torno dos pontos pesquisados. Nossa abordagem é radicalmente diferente desde que é baseada na simulação de Monte Carlo permitindo acompanhar os elétrons de energias menoress (~ 10eV) o que permite uma descrição nanométrica da física da radiação. As simulações numéricas foram então realizadas pelo modelo de desintegração completa de isotopos do iodo de vida curta assim como do Iodo-131 em tireóide de ratos recém nascidos na tentativa de obter resultados biológicos e histológicos de maior precisão para a glândula tireóide.