Radiobiology > Biologic Interactions > Cel Survival Curve > Curve Indices -- Quasi-Threshold Dose
Cell Survival Curve: Indices, continued
Another aspect of the curve is the so-called quasi-threshold dose (Dq). This is also known as the sub-lethal dose.
The quasi-threshold dose must be extrapolated from the curve:
- Begin by drawing a horizontal line (i.e. parallel to x-axis) from S=1.
- Now extend the straight portion of the survival curve back to the horizontal line from unity surviving fraction.
- The point of intersection is Dq.
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