Table 1.

Example of available physical dose derivation

Previous dose, Gy	EQD2, Gy	Repair, %	EQD2 with repair, Gy	Available EQD2, Gy	Available physical dose, Gy
27.50	31.63	50	15.81	34.19	28.98

Abbreviation: EQD2 = equivalent dose at 2 Gy per fraction.

Assume the patient had received 30 Gy in 10 fractions (27.5 Gy to the organ at risk) 21 months before the current course. The intended dose for the current course is 30 Gy in 10 fractions. The organ-at-risk limit is 50 Gy (maximum) and the α/β value used is 3 Gy. Note that the available physical dose is what is seen on the treatment planning system.