Induction of chromosome aberrations in human lymphocytes by technetium-99m. In vitro and in vivo studies
Jacquet, N.; Petiet, A.; Colas-Linhart, N. ; Guiraud-Vitaux, F.; Leroy, A.; Voisin, P
IRPA-10: 10. international congress of the International Radiation Protection Association Hiroshima (Japan) 14-19 May 2000, P2B-134
In Nuclear Medicine, total body dose calculated after a technetium 99m labeled pharmaceutical administration was very low. Nevertheless, risks evaluation of the radio-induced genetics damages at low doses has become a public health priority. Peripheral lymphocytes can be used to study the effects of ionizing radiations on human cells. The induction by ionizing radiations of unstable structural chromosome aberrations (dicentrics, centrics, and fragments) in peripheral blood lymphocytes is considered to be a useful technique to complete physical dosimetry, and presently is the most advanced biological dosimeter. The aim of the study was to evaluate the potential cytogenetic effects of in vitro and in vivo exposure to technetium 99m (99mTc). Firstly, to evaluate the level of 99mTc activity able to produce a significant number of unstable chromosomal aberrations, specific relationships between activity and number of unstable chromosomal aberrations was established in vitro. The whole blood in vitro irradiation procedure has been performed during 3 hours using microspheres labeled with increasing activities of 99mTc (0, 37, 74, 148, 296, and 444 MBq). Secondly, blood samples from 5 patients scheduled for benign bone disease scintigraphy were collected before and 6 hours after administration of 925 MBq of 99mTc-HDP. Both irradiated whole-blood samples obtained in vitro or in vivo are prepared for conventional scoring by classical Fluorescence Plus Giemsa. For in vivo study, 250 and 500 metaphases were scored respectively before and 6 hours after a bone scan undergone. For in vitro studies, 750 cells were scored per activity. The distribution of unstable chromosome aberrations after in vitro 99mTc irradiation follows a Poisson law. We observed no cytogenetic effect induced by clinical exposure to 99mTc 6 hours after administration versus the control point, as predicted by the in vitro results. Nevertheless, unstable anomalies are lethal to the cell and therefore are considered as a short-term biological dosimeter. Further investigations examining the stable aberrations such as translocations are presently being carried out in our laboratory to evaluate the potential genetic risks induced by administration of 99mTc radiopharmaceutical.