Convert any fractionation schedule into the equivalent dose delivered in 2 Gy fractions, so a hypofractionated course and a conventional one can be compared on the same scale for both tumour control and late normal-tissue effects.
The linear-quadratic model expresses biological effect as BED = D × (1 + d/(α/β)) and converts any schedule to the equivalent dose in 2 Gy fractions, EQD2 = BED / (1 + 2/(α/β)). EQD2 lets schedules with different fraction sizes be compared and summed. Typical α/β values are ~10 Gy for tumours and early-responding tissue, ~3 Gy for late-responding tissue, and ~1.5 Gy for prostate cancer.
The LQ model is well validated for conventional fraction sizes (about 1.8–5 Gy per fraction) and becomes unreliable for very large fractions such as single-fraction stereotactic treatments. Sources: Fowler, Br J Radiol 1989; Joiner & van der Kogel, Basic Clinical Radiobiology.
Enter the values for the scenario you are assessing. Convert any fractionation schedule into the equivalent dose delivered in 2 Gy fractions, so a hypofractionated course and a conventional one can be compared on the same scale for both tumour control and late normal-tissue effects. Use the eqd2 result to inform your calculation.