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Related Concept Videos

Pharmacodynamic Models: Linear Concentration–Effect Model01:15

Pharmacodynamic Models: Linear Concentration–Effect Model

The linear concentration–effect model, underpinned by the principle that pharmacological effect (E) is directly proportional to plasma drug concentration (C), emerges as a pivotal simplification of the Emax model for conditions where C is significantly less than EC50. This model portrays a linear trajectory of the concentration–effect relationship when drug levels are markedly below the EC50 threshold.Despite its inherent assumption of continuous effect augmentation with increasing drug...
Toxicity Testing in Animals01:23

Toxicity Testing in Animals

Toxicity tests in animals are grounded on two main assumptions: first, the effects observed in laboratory animals can be extrapolated to humans, especially when adjusted for body surface area; second, high-dose exposure in animals is essential to identify potential human hazards from lower doses. This is based on the quantal dose-response concept, which faces the challenge of extrapolating results from relatively few test animals to much larger human populations. For example, a 0.01% incidence...
Dose Response Curve: Conventional Versus Nonmonotonic01:21

Dose Response Curve: Conventional Versus Nonmonotonic

The correlation between a drug's dosage and its impact on a biological system is a cornerstone of pharmacology and toxicology. Conventional dose–response curves, which include graded and quantal relationships, are key to this understanding. Graded dose–response curves depict the spectrum of a biological reaction to different doses within an individual, indicating that as the drug dosage increases, so does the intensity of the response. On the other hand, quantal dose–response relationships...
Biological Effects of Radiation02:59

Biological Effects of Radiation

All radioactive nuclides emit high-energy particles or electromagnetic waves. When this radiation encounters living cells, it can cause heating, break chemical bonds, or ionize molecules. The most serious biological damage results when these radioactive emissions fragment or ionize molecules. For example, α and β particles emitted from nuclear decay reactions possess much higher energies than ordinary chemical bond energies. When these particles strike and penetrate matter, they produce ions...
Criteria for Causality: Bradford Hill Criteria - II01:28

Criteria for Causality: Bradford Hill Criteria - II

The Bradford Hill criteria serve as guidelines for establishing causative links in epidemiological research. Beyond Strength, Consistency, Specificity, and Temporality, key criteria also include Biological Gradient, Plausibility, Coherence, Experiment, and Analogy. These principles assist scientists in assessing the likelihood of causation in complex biological contexts. Below is a summary of these concepts:
Nonlinear Pharmacokinetics: Overview01:19

Nonlinear Pharmacokinetics: Overview

Nonlinear or dose-dependent pharmacokinetics is a phenomenon that occurs when the pharmacokinetic parameters of certain drugs deviate from linear pharmacokinetics at higher doses. These drugs do not follow the expected first-order kinetics, where the rate of drug elimination is directly proportional to the drug concentration. Instead, they exhibit a nonlinear relationship, which can be attributed to several factors.
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Related Experiment Video

Updated: Jul 5, 2026

Modeling Highly Repetitive Low-level Blast Exposure in Mice
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Modeling Highly Repetitive Low-level Blast Exposure in Mice

Published on: May 24, 2024

Low-dose radiation risk extrapolation fallacy associated with the linear-no-threshold model.

Bobby R Scott1

  • 1Lovelace Respiratory Research Institute, Albuquerque, New Mexico 87108, USA. bscott@LRRI.org

Human & Experimental Toxicology
|May 16, 2008
PubMed
Summary

The linear-no-threshold (LNT) model may overestimate cancer risk at low radiation doses. Low-dose radiation may decrease cancer risk through a protective apoptosis-mediated (PAM) process, challenging traditional LNT assumptions.

Related Experiment Videos

Last Updated: Jul 5, 2026

Modeling Highly Repetitive Low-level Blast Exposure in Mice
06:00

Modeling Highly Repetitive Low-level Blast Exposure in Mice

Published on: May 24, 2024

Area of Science:

  • Radiation biology
  • Radiobiology
  • Radiation protection

Background:

  • Radiation risk management traditionally relies on the linear-no-threshold (LNT) model.
  • The LNT model assumes stochastic effects, like cancer, increase linearly with dose without a threshold.
  • This model is widely used for extrapolating cancer risk from high to low radiation doses.

Purpose of the Study:

  • To provide indirect evidence questioning the validity of the LNT model at very low radiation doses.
  • To explore the potential for low-dose radiation to reduce cancer risk, contrary to LNT predictions.
  • To investigate the role of the protective apoptosis-mediated (PAM) process in radiation response.

Main Methods:

  • Review and analysis of indirect evidence regarding low-dose radiation effects.
  • Comparison of predicted risks from the LNT model with potential biological responses.
  • Examination of the dose-rate dependency and threshold for the PAM process activation.

Main Results:

  • Excess cancer risk predicted by LNT at very low doses (around 1 mGy) of low-linear-energy-transfer (LET) radiation may be a phantom risk.
  • Low-dose, low-LET radiation exposure (around 1 mGy) is more likely to decrease cancer risk than increase it.
  • The protective apoptosis-mediated (PAM) process, activated by low doses (as low as 0.01 mGy for X-rays/gamma rays), is implicated in this risk reduction, but not at very high doses (e.g., >250 mGy).

Conclusions:

  • The LNT model's extrapolation of high-dose cancer risks to low doses may be inaccurate.
  • A protective apoptosis-mediated (PAM) process offers a biological mechanism for cancer risk reduction at low, but not excessive, radiation doses.
  • Radiation protection regulations may need re-evaluation based on a more nuanced understanding of low-dose radiation effects and biological responses.