Nowadays proton therapy: Double scattering versus pencil beam scanning mode

Introduction Pencil beam scanning mode is becoming widely used in proton therapy. The biological consequences of the use of pencil beam scanning instead of double scattering mode have not been studied in detail yet. Most of the biological studies of relative biological effectiveness of protons were carried out using double scattering mode. The dose rates in pencil beam scanning are locally essentially higher than those in double scattering mode, which could affect the cell response. Purpose The main purpose of this study was to study the in vitro biological consequences of the use of pencil beam scanning in comparison to double scattering mode. Materials and methods Cell culture samples (normal human fibroblasts, medulloblastoma cell line DAOY) were irradiated by both modes using the same proton energies and doses. The initial energy of protons used for the irradiations was selected according to the clinical options in double scattering. The same energy was then adjusted for the pencil beam scanning mode. Several parameters (cell survival, apoptosis level, double strand break induction) of the cells were followed in various times post irradiation. Results The cell survival was found to be lower for the pencil beam scanning mode in both studied positions in the Bragg curve (plateau, peak). The apoptosis level and the induction of double strand breaks were found to be higher for pencil beam scanning mode. Conclusion We suggest that pencil beam scanning mode is slightly more efficient than double scattering mode. Disclosure No conflict.