Relative Biological Effectiveness (RBE)
The ratio of absorbed dose of a reference 250 kVp X-ray beam to the absorbed dose of a test radiation type required to produce an identical biological effect.
Governing formula
RBE = D_reference (250 kVp X-rays) / D_test (for equal biological effect)
SI unit
Dimensionless Ratio
In depth
High-LET radiation types (carbon ions, neutrons) have higher RBE values (>1 to 4) because dense ionizations create complex, unrepairable cell damage.
Examples in the real world
Carbon ion heavy ion therapy demonstrating an RBE ~3 near the Bragg peak compared to conventional X-rays.