Dose Rate Effect on Cell Survival in BNCT.

The output constancy of the accelerator used for boron neutron capture therapy (BNCT) is essential to ensuring anti-tumor efficacy and safety. BNCT as currently practiced requires a wide variety of beam quality assessments to ensure that RBE dose errors are maintained within 5%. However, the necessity of maintaining a constant beam dose rate has not been fully discussed. We therefore clarified the effect of different physical dose rates of the accelerator BNCT on biological effects. SAS and A172 cells exposed to 10 B-boronophenylalanine were irradiated using a neutron beam (normal operating current, 100 μA) at the Aomori Quantum Science Center. Thermal neutron flux was attenuated to 50.0 ± 0.96% under 50 μA irradiation compared to that under 100 μA irradiation. Cells were given physical doses of 1.67 and 3.36 Gy at 30 and 60 mC, respectively, and survival was significantly increased after 50 μA irradiation for both cell types ( p = 0.0052 for SAS; p = 0.046 for A172, for 60 mC). Differences in accelerator BNCT beam dose rates have non-negligible effects on biological effects. Dose rate fluctuations and differences should not be easily permitted to obtain consistent biological effects.