Biological consequences of irradiation by low doses of technetium 99m: Ultrastructural studies, p53 protein expression and cytogenetic effects

Few studies concerning the potential genetic effects of diagnostic radionuc lides used in nuclear medicine have been reported. The aim of this study wa s to evaluate the biological and cytogenetic consequences of two technetium 99m-labelled radiopharmaceuticals. Ultrastructural modifications of pulmon ary cells were first investigated after injection of Tc-99m labelled micros pheres in the rat. On the same irradiated cells, nuclear expression of p53 protein was assessed using immunohistochemistry. Despite very high previous ly calculated doses delivered,to pulmonary cells, no morpholological cell d amage and no significant increase of nuclear expression of the p53 were not ed. There was no correlation between the calculated dose and the ultrastruc tural biological damage. Secondly, a specific in vitro curve, activity/numb er of unstable chromosomal aberrations, corresponding to physical character istics of Tc-99m, was established to verify the potentiality of Tc-99m to i nduce such aberrations. In vivo, cytogenetic effects were assessed on blood samples of 5 patients with various arthrosic and periarthrosic diseases ob tained after bone scintigraphy. Aberration frequencies of both in vitro and in vivo irradiated lymphocytes were determined using the classical Fluores cence Plus Giemsa technique. No cytogenetic effects appeared with the routi nely Tc-99m injected activities as predicted by the in vitro curve.