The Experimental Measurement of the Relative Biological Effectiveness of Carbon Ions with Different Qualities

Abstract

The relative biological effectiveness (RBE) of carbon ions with linear energy transfer (LET) of 172 keV/µm and 13.7 keV/µm were determined in this study. The clonogenic survival and premature terminal differentiation were measured on normal human fibroblasts AG01522C and NHDF after exposure of the cells to 250 kV X-rays and carbon ions with different qualities. RBE was determined for these two biological end points. The results showed that the measured RBE10 with a survival fraction of 10% was 3.2 for LET 172 keV/µm, and 1.33 for LET 13.7 keV/µm carbon ions. RBE for a doubling of post-mitotic fibroblasts (PMF) in the population was 2.8 for LET 172 keV/µm, and 1 for LET 13.7 keV/µm carbon ions. For the carbon ion therapy, a high RBE value on the Bragg peak results in a high biological dose on the tumour. The tumour cells can be killed effectively. At the same time, the dose on healthy tissue would be reduced accordingly. This will lighten the late effect such as fibrosis on normal tissue.