Radiobiological Effects Induced by X-ray (LINAC) Irradiation: Experiments and Modelling

Abstract

In this study we present a modelling procedure that combines the standard electromagnetic physics of Geant4 for photons with the LEPTS event by event Monte Carlo simulation programme for secondary electrons. LEPTS provides detailed information of the energy deposition and the type and number of collision events taking place in a 1 m3 liquid water phantom when irradiated with 6 MV photons generated by a LINAC accelerator. The simulation is compared to a radiobiological experiment determining the biological effects (cell cycle alteration, early apoptosis, DNA damage) induced by the 6 MeV CLINAC radiation to a Jurkat T lymphocyte culture in a water phantom. Notable cell cycle alterations were found between 24 and 48 h after a 2 Gy radiation dose. Early apoptosis and DNA fragmentation has been analysed at 48, 72 and 96 h post irradiation. As expected, the sequence of the apoptotic process has been clear in the irradiated area up to 48 h after radiation. However, substantial apoptotic cells have also been identified outside of this area, in the penumbra and even in the low dose area, where a maximum in the percentage of DNA fragmentation is shown. We attributed this effect to the fact that although the average energy of primary and secondary particles in these areas is lower than those in the irradiated area, their interaction cross sections are much higher, thereby increasing the probability of producing damage.