CHROMOSOME-ABERRATIONS INDUCED IN HUMAN-LYMPHOCYTES BY 16.5 MEV PROTONS

In a track segment irradiation experiment with 16.5 MeV protons the induction of dicentrics was studied in human T-lymphocytes. The dose-response relationship was linear quadratic with estimated parameters α = (0.44 ± 0.07) × 10-1 Gy-1 and β = (1.95 ± 0.30) × 10-2 Gy-2. With respect to X-rays a limiting RBE of 1.1-1.2 exists. The present findings are compared with data from other laboratories obtained with 4.9 and 8.7 MeV protons. It was found that the data do not fit theoretical predictions on a proportional relationship between α values and LET. Using the microdosimetric quantity yD (25 nm), the dose average of the lineal energy, for characterization of these proton radiations, at a relevant site diameter of 25 nm the ratio of yD = 1.15 is in accordance only with the observed α ratio of 1.0 ± 0.23 for 8.7 and 16.5 MeV protons. In contrast to the prediction of a constant β at low LET values, the quadratic coefficients increase with increasing LET between 3 and 8 keV/μm. © 1990 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.