Induction of unstable and stable chromosomal aberrations by 99mTc: in-vitro and in-vivo studies

Biological dosimetry, which determines the dose of acquired radiation by measuring radiation-induced variation of biological parameters, can help assess radiation damage in an individual. Evaluation of radiation exposure requires setting up reference curves for each type of radiation.

To evaluate the potential induction of chromosome aberrations by a clinical diagnostic dose of 99mTc.

Dicentrics, rings, excess fragments, complete reciprocal translocations and incomplete reciprocal translocations were scored in peripheral blood lymphocytes from patients exposed to a 99mTc bone scintigraphy. A specific relationship between the radiation dose delivered by 99mTc and the frequency of stable and unstable chromosomal aberrations was established in vitro to estimate whole-body dose. Chromosome analysis using fluorescence plus Giemsa and fluorescence in-situ hybridization was undertaken on six patients before and after a 99mTc bone scintigraphy. Dicentrics, rings, excess fragments, and translocations were scored in blood lymphocytes after in vitro 99mTc external irradiation in order to construct dose calibration curves.

Analysis of the in-vitro data shows that the number of both unstable and stable aberrations has a quadratic linear relationship to the dose. Our in-vivo irradiation studies showed that activities of 99mTc-hexamethylene diphosphonate (99mTc-HDP) used for bone investigations do not induce any additional unstable chromosome aberrations and translocations. The frequencies obtained did not differ significantly from background values.

99mTc can produce unstable and stable chromosomal aberrations in vitro. 99mTc-HDP administration does not induce supplementary chromosomal aberrations. The dose-response curves will allow a more accurate evaluation of the risk related to in-vivo administration of 99mTc labelled radiopharmaceuticals, and they can be used to assess the safe upper limit of injected activity in humans.