title: An in vitro study of the radiobiological effects of flattening filter free radiotherapy treatments.
abstract: Flattening filter free (FFF) linear accelerators allow for an increase in instantaneous dose-rate of the x-ray pulses by a factor of 2-6 over the conventional flattened output. As a result, radiobiological investigations are being carried out to determine the effect of these higher dose-rates on cell response. The studies reported thus far have presented conflicting results, highlighting the need for further investigation. To determine the radiobiological impact of the increased dose-rates from FFF exposures a Varian Truebeam medical linear accelerator was used to irradiate two human cancer cell lines in vitro, DU-145 prostate and H460 non-small cell lung, with both flattened and FFF 6 MV beams. The fluence profile of the FFF beam was modified using a custom-designed Nylon compensator to produce a similar dose profile to the flattened beam (6X) at the cell surface but at a higher instantaneous dose-rate. For both cell lines there appeared to be no significant change in cell survival. Curve fitting coefficients for DU145 cells irradiated with constant average dose-rates were 6X: α = 0.09 ± 0.03, β = 0.03 ± 0.01 and 6FFF: α = 0.14 ± 0.13, β = 0.03 ± 0.02 with a significance of p = 0.75. For H460 cells irradiated with the same instantaneous dose-rate but different average dose-rate the fit coefficients were 6FFF (low dose-rate): α = 0.21 ± 0.11, 0.07 ± 0.02 and 6FFF (high dose-rate): α = 0.21 ± 0.16, 0.07 ± 0.03, with p = 0.79. The results indicate that collective damage behaviour does not occur at the instantaneous dose-rates investigated here and that the use of either modality should result in the same clinical outcome, however this will require further validation in vivo.
authors: Radiotherapy Physics, Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, BT9 7AB, UK.
authors: R B
authors: RB
authors: King
authors: W B
authors: WB
authors: Hyland
authors: A J
authors: AJ
authors: Cole
authors: K T
authors: KT
authors: Butterworth
authors: S J
authors: SJ
authors: McMahon
authors: K M
authors: KM
authors: Redmond
authors: C
authors: C
authors: Trainer
authors: K M
authors: KM
authors: Prise
authors: C K
authors: CK
authors: McGarry
authors: A R
authors: AR
authors: Hounsell
mesh_terms: D045744:Cell Line, Tumor; D002470:Cell Survival / Q000528:radiation effects; D006801:Humans; D008297:Male; D011853:Radiobiology; D011874:Radiometry; D011879:Radiotherapy Dosage; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D013997:Time Factors