INVITRO RADIOSENSITIVITY OF HUMAN TUMOR-CELLS EXPOSED TO HEAVY-CHARGED PARTICLES

Although the response of human tumour cell lines to low linear energy transfer (LET) radiation is largely documented, little is known about the effect of heavy charged particles on these lines. We have exposed a melanoma cell line (CAL 1), a breast carcinoma cell line (CAL 51) an d a neuroblastoma cell line (CHP 100) to 11 MeV Ne particles (400 KeV/ mum), 14 MeV Ar (900 KeV/mum), 7 MeV Ar (1500 KeV/mum), 13 MeV Kr (400 0 KeV/mum), and 11 MeV Au (9000 KeV/mum), using the facilities of Unil ac at GSI, Darmstadt. Survival curves were constructed and the respons e. assessed by the in vitro colony survival, was compared to that foll owing Cobalt irradiation. As the LET increases, the beta component of the survival curve becomes smaller or even absent, indicating a prepon derance of single-hit inactivation. At very high LET values, a below o ne extrapolation number was noticed, suggesting the presence of either subpopulations with different sensitivities or inhomogeneities in the dose distribution. With these particles and energies, the efficiency steadily decreased with increasing LET, leading to reduction of the re lative biological effectiveness (RBE). Only with 11 MeV Ne and with 14 MeV Ar was the RBE, measured at 0.1 survival, greater than one. The l ower the alpha term of the low LET survival curve and the higher the b eta term, the higher the RBE. The bigger the nuclear area of the expos ed cells, the steeper the initial slope of particle irradiation, for p articles having LET values up to about 1000 KeV/mum. Finally, whatever the cell line and the particle, there was an inverse relationship bet ween RBE and dose.