MOD 4 - Radiosensitivity

influencing factors of the susceptibility to injury

• cell differentiation

• cell development stage

• organism development phase

relationship between cell diff and radiosensitive

cellular radiosensitivity is inversely proportional to the degree of cell differentiation

relationship between radiosensitivity and cell division

cellular radiosensitivity is directly proportional to the rate of cell division

cell development stage effect on radiosensitivity

immature cells or actively dividing cells at higher risks

phase of organism development effect on radiosensitivity

growth phase is more susceptible due to ongoing cellular division to support growth

Cellular radiosensitivity level (high to low)

1. Hematopoietic, Reproductive Systems, Lymphatic Systems

2. GI  Systems

3. Epidermal tissues and Eyes

4. Support and Nervous System

two general components of tissues and organs

• parenchymal compartment

• stromal compartment

parenchymal compartment

contains cells characteristic of that specific tissue or organ

stromal compartment

• makes up supporting structure

• no specialized function

which compartment is more radiosensitive and why

parenchymal as they are highly differentiated with a high rate of mitosis

inherent cellular radiosensitivity considers…

the biologic factors that are characteristics of the cells themselves

eg. inherent cellular radiosensitivity

• mitotic rate

• degree of differentiation

• cell cycle stage

when does the probability of direct effects to the cell increase

during mitosis, as high mitotic rate within a tissue naturally increases the relative radiosensitivity

Bergonie and Tribondeau Law indiactes that

• Radiosensitivity is the relative susceptibility of cells, tissues, organs, and organisms, or any living substance, to the injurious action of radiation

• radiosensitivity of cells is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation

• radiosensitivity is a function of the metabolic state of the tissue being irradiated

• weighting factors for the various regions/organs of the body have been established to allow for effective dose estimates for all radiologic examinations.

Radiosensitivity of Tissues and Organs are independent on

the organs location or size

fetus and child are highly radiosensitive due to

• higher ratio of immature cells

• increased proportion of stem cells

• high rate of mitosis

• relative age of the tissues

Effects of Radiation Exposure on Preimplantation

embryonic death

Effects of Radiation Exposure on Organogenesis

congenital abnormalities that may result in neonatal death

Effects of Radiation Exposure on Fetal

childhood cancers and functional disorders

Children are more radiosensitive because

• their smaller bodies increases resultant internal dose

• longer life expectancy is much longer which allows time for long term effects of radiation exposure to become manifested

Oxygen enhancement Ratio (OER)

captures the linear relationship between the level of tissue oxygenation and the potential for radiation damage

the oxygen effect describes

highly oxygenated tissue is more sensitive to radiation exposure than low oxygenated tissue

high LET radiation has an OER of

biologic impacts are increased by 1x in highly oxygenated tissues

low LET radiation has an OER of

biologic impacts are increased by 2.5-3x in highly oxygenated tissues

relationship between DNA and oxygen

DNA’s ability to repair from indirect free radical damage is reduced by the presence of molecular oxygen

Radiation Factors Affecting Radiosensitivity

• LET

• Relative Biological Effectiveness (RBE)

RBE is

the effectiveness of the radiation dose