Cell Survival Curves Flashcards
Reproductive Death
Loss of the ability to divide indefinitely
Relevant Doses
100 Gy - destroys cell function in non-proliferating systems
2 Gy - mean lethal dose for loss of proliferative capacity
In-Vitro
Studies performed on cells outside of their biological context (in petri-dishes)
Clonogenic Cells
Cells that have retained reproductive integrity and is able to proliferate indefinitely
Survival Curve
Describes the relationship between radiation dose and the fraction of cells that survive that dose
Plating Efficiency
Percentage of cells, in the control batch, that grow into colonies
Surviving Fraction
Fraction of cells that plate successfully and survive irradiation
(Colonies Counted) / (Cells Seeded x Plating Efficiency/100)
Relationship between survival curves and LET
As LET increases:
- Slope of curve increases
- Curve becomes more linear on semi-log plot
- Shoulder disappears
2 General Cell Survival Models
Linear Quadratic Model
Multi-target Model
Linear Quadratic Model
First component - cell killing is proportional to dose for damage caused by a single event
Second component - cell killing is proportional to dose squared for damage caused by multiple events
Multi-target Model
Based on the probability of hitting the target
Initial slope is due to single-event killing and final slope is due to multiple-event killing
Bystander Effect
Induction of biological effects in cells not directly traversed by a charged particle but in close proximity to the charged particle
Appears mainly at low doses
Cause of Bystander Effect
Cytotoxic materials produced in irradiated cell is released into bystander cells via gap-junction communication medium and cause bystander cell death
Apoptotic (Programmed) Cell Death
Cell ceases to communicate with neighbors
Cell detaches from neighbors
Chromatin condenses at nuclear membrane
Fragmentation of nucleus
Cell shrinks and separates into membrane bound fragments
Little or no dose-rate effect
Mitotic Cell Death
Most common form of cell death following radiation exposure
Results from exchange type aberrations
Cells die attempting to divide with damaged chromosomes
Substantial Dose Rate Effect