In vitro irradiation of blood with 99mTc: evaluation of dose and chromosome aberrations in irradiated lymphocytes.

The use of ionizing radiation for diagnostic or therapeutic purposes in medicine represents the principal source of artificial radiation to humans. Calculation of radiation dose is essential to the analysis of risks (biological effects) and benefits in any application, including nuclear medicine. The dose assessment in many cases is not necessarily straightforward. Many radiopharmaceuticals are labelled with radionuclides that undergo not only gamma-emission but also emission of Auger and internal conversion electrons. A typical example is technetium-99m (99mTc), which is used in more than 80% of nuclear medicine applications. In this work, in vitro studies have been carried out to evaluate the dose delivered to lymphocytes by human serum albumin microspheres (HSAM) labelled with 99mTc. Experiments were performed in order to score unstable chromosomal aberrations induced by 99mTc-HSAM, using conventional cytogenetic techniques. Henceforth, the relationship between activities introduced into blood samples and induced chromosomal aberrations were evaluated. To assess the dose absorbed in lymphocytes, electron and photon transport was performed in a simple model representing the system used for irradiating the cells using the MCNP Monte Carlo code. In this report, analysis of dose-effect curve demonstrates a linear quadratic response for unstable chromosome aberrations.