05 Biology
Oxygen enhancement ratio
Hypoxic dose over aerated dose for the same effect.
Listen
Listen · English
Simulation
Oxygen enhancement ratio — Change the numbers; the scene follows.
Where it works
Linear accelerator
Isocenter
In the treated volume — tumour and OARs at isocenter, after the dose has been delivered.
Open this machineFormula
Variables
Results
OER
Oxygen enhancement ratio
3
Explanation
What it means
Oxygen enhancement ratio is hypoxic dose over aerated dose for the same survival. Photons have OER ~ 2.5–3 at high dose; it falls toward 1 at very low dose and for high-LET radiation (a rationale for carbon ions in hypoxic tumours). This is a working relation in Radiobiology.
Where it is used
Clinically it sits on the Linear accelerator — Isocenter. In the treated volume — tumour and OARs at isocenter, after the dose has been delivered. Radiobiology sits between the prescription and the organ-at-risk: LQ, BED, EQD2, and why 2 Gy is not 2 Gy if the fraction size changed. Use it to compare regimens, not to invent one.
Linear accelerator · Open this machineHow to use it
Enter the two isoeffective doses from a cell-survival experiment (or a model). Clinical ‘hypoxic load’ is more complex (intermittent hypoxia, reoxygenation). Change one input and watch the curve and the simulation follow.
Symbols
- D_hHypoxic dose6 Gy
- D_aAerated dose2 Gy
Worked example
A typical case from the default values: D_h = 6 Gy (Hypoxic dose); D_a = 2 Gy (Aerated dose). Substituting into the relation gives OER = 3. These are teaching numbers — align them with your machine.
Typical values give
- OER = 3
Where it comes from
The displayed formula is the working relation. Hypoxic dose over aerated dose for the same effect. Usual reference: Hall & Giaccia. Derive it in the specialty lesson, then return here to pin the numbers.
Reference: Hall & Giaccia
Assumptions & limits
Single-dose in-vitro definition. In vivo OER is modified by reoxygenation between fractions.
Pitfalls
α/β is a model parameter, not a measured organ. BED from incomplete repair or a changed overall time is not the simple n·d·(1+d/(α/β)). Never EQD2 a stereotactic dose with an α/β you did not state. Single-dose in-vitro definition. In vivo OER is modified by reoxygenation between fractions.
Keep this
Always write α/β and the fraction size next to a BED or EQD2. Single-dose in-vitro definition. In vivo OER is modified by reoxygenation between fractions.
In this specialty