What is the relationship between parameters used to characterize the sigmoidal dose response curve?
Radiation Physics
Prescribing, Reporting, and Evaluating Radiation Therapy Treatment Plans
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The dose response curve relates the probability of a response to the dose. The "response" can be either tumor control or normal tissue complication. The probability of a response ranges from 0 when the dose is negligible to 1.0 when the dose is large.
These curves have a sigmoidal shape and are described by two parameters: D50 and γ50. D50 is the dose at which the probability of a response is 50%. γ50 is the slope of the line tangent to the linear portion of the curve at D50 multiplied by the value of D50. γ50 is a measure of the steepness of the dose response curve.
Source: McDermott and Orton The Physics & Technology of Radiation Therapy 2nd ed. Chap. 14
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