Monte Carlo simulation for assessing absorbed dose effects of low-dose ß-radiation (90Sr/90Y) on cytotoxicity and apoptotic death in K562 cells.

Objective: Most studies suggest that dose-specific radiation regimens are essential for optimal induction of cancer cell response. This study focused on determining ß-radiation-absorbed dose (rad) effects on the cell viability, cytotoxicity, hypersensitivity, and cell death of K562 cells using experimental methods and Monte Carlo simulation (MCS). Materials and Methods: The K562 cells were cultured and irradiated with ß-particles emitted from a strontium source in vitro, with the estimated daily activity of 1.238 µCi. The treated cells were radiated at least three times every day for 3 consecutive days. The cell viability and apoptosis were investigated in treated cells by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, DNA electrophoresis, Hoechst dye, and inverted microscope. The average absorbed doses were obtained by MCS (MCNPX code). To verify simulation and experimental results, we used a Geiger-Muller counter and estimated a scaling factor. Results: The cytotoxic effects and cell death were induced in the treated groups via rad in a time-dependent manner. The highest apoptotic and cytotoxic effects were observed in cells after irradiation with ß-particles for 120 min per day in 3 consecutive days. rads were determined using MCNPX code and cell survival rates were significantly reduced during irradiation periods. No significant hyper-radiosensitivity was found based on experimental and theoretical results. Conclusion: Despite the difficult calculation of the rad in the target cells and the scant information in this field, fortunately we have achieved significant theoretical data consistent with the experimental results. Our findings also introduced MCS as a better choice for evaluating of rad effects under different cellular conditions with high accuracy.

Diaphragm correction factors for the FAC-IR-300 free-air ionization chamber.

A free-air ionization chamber FAC-IR-300, designed by the Atomic Energy Organization of Iran, is used as the primary Iranian national standard for the photon air kerma. For accurate air kerma measurements, the contribution from the scattered photons to the total energy released in the collecting volume must be eliminated. One of the sources of scattered photons is the chamber's diaphragm. In this paper, the diaphragm scattering correction factor, kdia, and the diaphragm transmission correction factor, ktr, were introduced. These factors represent corrections to the measured charge (or current) for the photons scattered from the diaphragm surface and the photons penetrated through the diaphragm volume, respectively. The kdia and ktr values were estimated by Monte Carlo simulations. The simulations were performed for the mono-energetic photons in the energy range of 20 - 300keV. According to the simulation results, in this energy range, the kdia values vary between 0.9997 and 0.9948, and ktr values decrease from 1.0000 to 0.9965. The corrections grow in significance with increasing energy of the primary photons.

INVESTIGATION OF THE HUMIDITY EFFECT ON THE FAC-IR-300 IONIZATION CHAMBER RESPONSE.

The free-air ionization chamber is communicating with the ambient air, therefore, the atmospheric parameters such as temperature, pressure and humidity effect on the ionization chamber performance. The free-air ionization chamber, entitled as FAC-IR-300, that design at the Atomic Energy Organization of Iran, AEOI, is required the atmospheric correction factors for correct the chamber reading. In this article, the effect of humidity on the ionization chamber response was investigated. For this reason, was introduced the humidity correction factor, kh. In this article, the Monte Carlo simulation was used to determine the kh factor. The simulation results show in relative humidities between 30% to 80%, the kh factor is equal 0.9970 at 20°C and 0.9975 at 22°C. From the simulation results, at low energy the energy dependence of the kh factor is significant and with increasing energy this dependence is negligible.