RTH-03

Equivalent dose in 2 Gy fractions

EQD2 = D (d + α/β)/(2 + α/β). The 2 Gy-fraction isoeffect.

Reading speed

RadiobiologyEQD2Withers

Governing equation

\mathrm{EQD}_{2}=D\dfrac{d+\alpha/\beta}{2+\alpha/\beta}

where

D: Total dose (Gy)
d: Dose per fraction (Gy)
\alpha/\beta: α/β (Gy)
EQD_{2}: EQD2 (Gy)

Lecture brief

Historical brief

The linear-quadratic model, BED, tissue-maximum ratio and Clarkson scatter turned radiotherapy into fraction arithmetic. MU calculation on these sheets is that clinical closed form. This sheet (RTH-03 — Equivalent dose in 2 Gy fractions) is the form associated with EQD2 · Withers. Working symbols: $D$ , $d$ , $\alpha/\beta$ $\rightarrow$ $EQD_{2}$ . Converts any schedule to a 2 Gy/fraction standard so trials can be compared.

Purpose

Purpose: compute

EQD_{2}

from

D

d

\alpha/\beta

in Radiotherapy via

\mathrm{EQD}_{2}=D\dfrac{d+\alpha/\beta}{2+\alpha/\beta}

EQD2 = D (d + α/β)/(2 + α/β). The 2 Gy-fraction isoeffect. Use it when a real radiotherapy question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

D = 60.000\,\mathrm{Gy}

d = 2.000\,\mathrm{Gy}

\alpha/\beta = 10.000\,\mathrm{Gy}

, the governing relation

\mathrm{EQD}_{2}=D\dfrac{d+\alpha/\beta}{2+\alpha/\beta}

yields

EQD_{2} = 60.00\,\mathrm{Gy}

. A dose bar rescaled onto a 2 Gy grid. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Total dose D60 GyDose per fraction d2 Gyα/β \alpha/\beta10 Gy

Outputs

EQD2 EQD_{2}60.00 Gy

Reading speed

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Narration of this film

A dose bar rescaled onto a 2 Gy grid.

Converts any schedule to a 2 Gy/fraction standard so trials can be compared.

Reading speed

Watch on YouTube