Chromosome aberrations in human lymphocytes from the plateauregion of the Bragg curve for a carbon-ion beam

Radiotherapy with high-energy carbon ion beams can be more advantageous compared to photons because of better physical dose distribution and higher biological efficiency in tumour cell sterilization. Despite enhanced normal tissue sparing, damage incurred by normal cells at the beam entrance is unavoidable and may affect the progeny of surviving cells in the form of inheritable cytogenetic alterations. Furthermore, the quality of the beam along the Bragg curve is modified by nuclear fragmentation of projectile and target nuclei in the body. We present an experimental approach based on the use of a polymethylmethacrylate (PMMA) phantom that allows the simultaneous exposure to a particle beam of several biological samples positioned at various depths along the beam path. The device was used to measure the biological effectiveness of a 60 MeV/amu carbon-ion beam at inducing chromosomal aberrations in G0-human peripheral blood lymphocytes. Chromosome spreads were obtained from prematurely condensed cells and all structural aberration types were scored in Fluorescence in situ Hybridization (FISH)-painted chromosomes 1 and 2. Our results show a marked increase with depth in the aberration frequency prior to the Bragg peak, which is consistent with a linear energy transfer (LET)-dependent increase in biological effectiveness.