The aim of this study was to investigate the radiobiological effects of flattening
filter (FF) and flattening filter-free (FFF) modes of linear electron accelerators
and to understand whether there is any difference between the effects of these modes.
We evaluated the number of chromosome aberrations following irradiation of lymphocytes
from healthy volunteers with X-ray photons at two energy levels, 6 and 10 MV; the
dose rate ranged between 5.50 and 23.08 Gy/min and absorbed doses ranged between 0.5
and 8 Gy. A 60Co curve was employed for comparison. Metaphases from the lymphocyte
cultures were prepared using standard cytogenetic techniques and chromosome analysis
was performed. Our results allow the performance of biodosimetry at higher energies
and doses than the currently used reference dosimetry. We observed significant differences
in aberration frequencies when different irradiation techniques were used. FFF mode
has a higher radiobiological effect than the FF mode. Linear-quadratic dose response
calibration curves were constructed and relative biological effectiveness (RBE) values
were calculated. Average RBE values using 6 MV (5.50 Gy/min) as a reference radiation
were 1.28 for 60Co γ irradiation, 1.11 for 6 FFF and 0.79-0.92 for 10 FFF. Since there
are compelling differences between radiation modalities in cases of hypofractionation,
these results may be even more important in a therapeutic situation. In case of an
accidental overdose of a patient, use of the appropriate calibration curves for biodosimetry
are also essential for quantifying the overdose.
