Killing of Feline T-Lymphocytes by Gamma-Rays and Energetic Carbon Ions

抄録

High linear energy transfer (LET) heavy charged particles have previously been applied clinically to human cancer radiotherapy because of their excellent physical properties of selective dose distribution and higher relative biological effectiveness (RBE) for human; however, such an approach has yet to be applied to cat patients. The present study investigates the biological effectiveness of low-LET γ-rays (0.2 keV/μm) compared to high-LET carbon ions (114 keV/μm) in feline T- lymphocyte FeT-J cells. Clonogenic survival analysis revealed that the RBE value of carbon ions was 2.98 relative to a 10% survival dose (D₁₀) by γ-rays, and that the inactivation cross-section in cells exposed to γ-rays and carbon ions was 0.023 and 38.9 μm², respectively. Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) analysis revealed that TUNEL-positive frequency in carbon-irradiation cells is higher than for γ-irradiated cells against exposure to the same physical doses, but that very little difference in TUNEL-positive frequency is observed between cells exposed to the respective D₁₀ dose of γ-rays. Our data thus indicate that carbon ions are more effective for cell killing than γ-rays at the same physical doses, but kill cells to an extent that is comparable to γ-rays at the same biological doses. Carbon ion radiotherapy is therefore a promising modality for cat patients.