Studies on variation of relative biological effectiveness with dose using 8 MeV pulsed electron beam from Microtron Accelerator

Radiation plays an important role in life science and medicine. The ionizing radiation, which deposits energy from its interaction with biological material, is a potent inducer of DNA damage due to both free radical formation and direct DNA interactions. Equal physical doses of different types of radiation do not produce equal biological effects because of differences in their energy deposition patterns. This is taken into account by the concept of relative biological Effectiveness (RBE). The consideration of RBE ensures that radiation oncologists can benefit from the large clinical experience gained with photon beams. Relative biological effectiveness (RBE) compares the severity of damage induced by a radiation under test, at a dose DT relative to the reference radiation dose DR for producing same biological effectiveness. The reference radiation is usually 220 kVp X-ray or 60Co γ photons. RBE varies as a function of radiation dose, the temporal pattern in which dose is received, dose rate, energy of the radiation, the level of the effect and biological endpoint studied. RBE is an important parameter in the estimation of risk from exposure to ionizing radiation. At present, the use of electron beam is constantly gaining importance in therapeutic applications. It offers many advantages over conventional 60Co teletherapy, such as better dose profile and drastic reduction in dose to the normal tissues beyond the tumor. The present study, the RBE of 8 MeV pulsed electron beam was estimated using using Saccharomyces cerevisiae D7. An attempt was made to understand the variation of RBE as a function of radiation dose, with theoretical considerations. The study confirms that, electron beam induces more damage at lower doses and at higher doses induction of damage is comparable to that of gamma radiation. (author)