21 years of biologically effective dose

Review by the originator of the term biologically effective dose (BED, introduced in Br J Radiol in 1989). Gives the BED formula — nd[1 + d/(α/β)], with an optional overall-time term — and the conversion to the equivalent dose in 2 Gy fractions by dividing BED by 1 + 2/(α/β) (1.2 for α/β = 10 Gy, 1.67 for 3 Gy, 2.0 for 2 Gy). Its worked example: 30 × 2 Gy = 60 Gy is 72 Gy10 to early-responding tissue and 100 Gy3 to late-responding tissue, but 60 Gy EQD2 to both. Full text read in Europe PMC (PMC3473681).

The author of the BED concept explains the formula, its units (Gy10, Gy3), how to convert BED to EQD2, and why BED must not be confused with an equivalent dose.