Adaptive response and human benefit: Part I. A microdosimetry dose-dependent model.

Area of Science:

• Radiation biology
• Biophysics
• Cellular and molecular biology

Background:

• Adaptive response to ionizing radiation is a complex phenomenon with potential human health benefits.
• Understanding the precise mechanisms and thresholds for adaptive response is crucial for risk assessment.
• Existing models may not fully capture the microdosimetric events leading to cellular responses.

Purpose of the Study:

• To develop and apply a microdosimetric dose-response model for evaluating adaptive response to ionizing radiation.
• To explicitly determine the threshold for activation of protective mechanisms against radiation damage.
• To analyze cellular negative response behavior under broad beam exposures.

Main Methods:

• Developed a biophysical model quantifying microdose specific energy deposition in cell nucleus volumes.
• Applied the model to existing adaptive and non-adaptive response data from multiple studies.
• Quantified Poisson-distributed microdose specific energy hits to cell critical nucleus volumes.

Main Results:

• The model accurately fits adaptive and non-adaptive radiation response data.
• One to two low linear energy transfer (LET) hits activate protective mechanisms against spontaneous and radiation damage.
• Dose plateau observed for radon progeny alpha-induced chromosome aberrations; bystander effect is dose-rate dependent for alpha particles.

Conclusions:

• The microdosimetry model precisely determines specific energy hits activating cellular protective and damage mechanisms.
• Minimal low LET hits can reduce spontaneous and radiation-induced damage, highlighting adaptive response benefits.
• The model aids in comparing different exposure scenarios (in vitro/in vivo, broad beam/microbeam) and assessing radioprotective thresholds.