LAW OF BERGONIE & TRIBONDEAU, PHYSICAL & BIOLOGICAL FACTORS THAT AFFECT RADIOSENSITIVITY Flashcards
Who promulgated the law of Bergonie and Tribondeau
Jean Alban Bergonie & Louis Tribondeau
State the Law of B&T
Radiosensitivity of living tissue varies with maturation and metabolism
When was the Law of B&T created?
1906
What are the 4 physical factors that affect radiosensitivity?
Linear Energy Transfer
Relative Biologic Effectiveness
Protraction
Fractionation
The measure of the rate at which energy is transferred from ionizing radiation to soft tissue.
Linear Energy Transfer
What is the unit used to express Linear Energy Transfer?
expressed in units of kiloelectron volt of energy transferred per micrometer of track length in soft tissue (keV/µm).
As the LET of radiation increases, the ability to produce biological damage also increases.
Relative Biologic Effectiveness
As the LET increases, RBE _______
also increases
What is the exception made in RBE?
There is a max value of RBE followed by a lower RBE because of overkill
What is the LET of xrays?
approx 3 keV/um
What is the RBE of xrays?
1
dose of radiation is delivered over a long period of time rather than quickly, the effect of that dose is less
Protraction
dose of radiation is given at equal fractions in different times
Fractionation
Why is fractionation more preferred than protraction?
Radiation dose fractionation reduces effect because cells undergo repair and recovery between doses
What are the different biologic factors that affect radiosensitivity?
Oxygen effect Age Recovery Chemical Agents Hormesis
Tissue is more sensitive to radiation when irradiated in the oxygenated, or aerobic state than when irradiated under anoxic or hypoxic conditions
oxygen effect
How do you describe the oxygen effect numerically?
oxygen enhancement ratio (OER)
This biological factor states that humans are most sensitive before birth.
age
After birth, sensitivity _____ until maturity, at which time humans are most resistant to radiation effects. In old age, humans again become somewhat more radiosensitive
decreases
This states that human cells can recover from radiation damage only if the radiation dose is not sufficient to kill the cell before its next division - Interphase death.
recovery
If given enough time, the cell will recover from the sublethal radiation damage it has sustained by ____________
cell repopulation
recovery = _____ + _____
intracellular repair + repopulation
this states that Some chemicals can modify the radiation response of cells, tissues, and organs. For chemical agents to be effective, they must be present at the time of irradiation. The post-irradiation application does not usually alter the degree of radiation response
Chemical agents
what are the two types of chemical agents?
radiosensitizers
radioprotectors
Difference between radiosensitizers and radioprotectors?
RS - Agents that enhance the effect of radiation are called sensitizing agents
RP - Radioprotectors are compounds used to protect the non-tumor cells from the harmful effects of radiation
What is hormesis?
It refers to the radiobiologic evidence that a little bit of radiation is good for the body because it stimulates hormonal and immune responses to other toxic environmental agents
