They theorized and observed that radiosensitivity was a function of the metabolic state of tissue being
irradiated.
Jean Alba Bergonie, Louis Tribondeu
law states that the
radiosensitivity of tissue varies within maturation and metabolism
law of radiosensitivity
In diagnostic imaging, the law serves to remind us that the fetus is considerably more sensitive to radiation exposure THAN the child or mature adult.
law has found some application in radiation oncology
LAW OF BERGONIE AND TRIBONDEAU
In, ____ radiologist Jean Alba Bergonie and physician Louis Tribondeau observed the effects of radiation by exposing _
1906, rodent testicles to X-rays.
modified law of bergonie and tribondeau
Paul Ancel (emryologists)
P. Vitemberger
- suggested that the intrinsic
susceptibility of damage to any cell by ionizing radiation is identical, but that the timing of manifestation of radiation-produced damage varies according to the cell type. - determined that a given dose of radiation will cause the same degree of damage to all cells, but only if and when the cell divides will damage be demonstrated.
law of ancel and vitemberger
- few specialized morphologic or
functional characteristics. - an immature cell whose primary
function is to divide, thus providing cells a way to maintain its population and to replace mature cells lost from the end population. - It is considered precursor or stem cell in a population.
UNDIFFERENTIATED CELL
- one which is specialized functionally
and/or morphologically. - considered a mature cell or end cell in
a population.
DIFFERENTIATED CELL
refersto the sum processes whereby
undifferentiated cells become specialized functionally and/or morphologically (structurally
differentiation
HIGHLY RADIOSENSITIVE
● Lymhoid tissue
● Bone Marrow
● Gastrointestinal
epithelium
● Gonads
● Embryonic tissues
MODERATELY RADIOSENSITIVE
● Skin
● Vascular
endotheliumlung
● Kidneyiver
● Lens (eye)
LEAST RADIOSENSITIVE
● Cetral nervous system
● Muscle
● Bone Cartilage
● Connective tissue
Dose which would cause death to
50% of the population in 30 days.
Its value is about 2-3 Gy for humans for whole body irradiation
LETHAL DOSE 50/30
LET
linear energy transfer
generally causes sublethal damage to DNA, repair enzymes can usually reverse the cellular damage.
low LET radiation
causes multi-strand breaksin DNA, repair enzymes are not effective at undoing this damage, and hence cell death will probably occur.
high LET radiation
- Allows for less effect
because the body can have time for repair of cellular organisms as well as recovery of tissues affected. - Even though the same dose is delivered to two different individuals, if it is delivered more quickly to one of them, it will cause more harm
protraction
- division of large doses
of radiation needed for treatment into smaller radiation doses (usually daily increments). - Reduces effect because cells undergo repair and recovery between doses.
- Used in radiation therapy since it allowstime for tissue repair and recovery between the radiation treatments.
fractionation
most radiosensitive phase of the cell cycle is _ . _ is also considered to be radiosensitive.
M, G2
The most
resistant phase is late _. _ is also considered to be radioresistant.
S, G1
- agents that enhance the
effect of radiation. - these drugs make the
individual about twice as sensitive to radiation than normal
Radiosensitizers
- agents that reduce the effects of radiation upon cells.
- group of chemicals called _______ have a radioprotective effect, but are too toxic for human use.
radioprotectors, sulfhydrils
five R’s
repair
reoxygenation
repopulation
redistribution
radiosensitivity
the process of rejoining DNA strands.
repair
