L9- Radiobiological Principles in Radiation Therapy

Bergonie

Tribondeau

In 1906, two French scientists theorized and observed that radiosensitivity was a function of the metabolic state of tissue being irradiated.

Law of Radiosensitivity

the law states that the radiosensitivity of tissue varies within maturation and metabolism

rabbit testicles

Supported by their observations using ___, they proposed a law describing radiation sensitivity for all body cells which is the Law of Bergonie and Tribondeau.

Law of Radiosensitivity

Their law maintains that actively cells mitotic and are most undifferentiated susceptible to damage from radiation

1. Have a high mitotic rate (divide rapidly)

2. Are less differentiated (more primitive/immature)

3. Have a long dividing future (many divisions ahead

The law states that cells are more sensitive to radiation if they:

RADIOSENSITIVITY

-the relative susceptibility of cells, tissues, organs, organisms, or other substances to the injurious action of

radiation.

Radiation therapy

is most effective when a tumor is contained, easily accessible, and located away from major organs of the body

Oligometastatic tumors

can be considered for curative treatment

Radiocurability

means that the normal tissue tumor relationship is such that curative doses of radiation can be used without excessively damaging the normal tissue

Radiocurative tumors

include carcinoma of the cervix, larynx, breast, and prostate.

Fractionation

is the process of delivering the total prescribed radiation dose in multiple smaller doses (fractions) over a period of time, rather than giving it all at once

Fractionation

Dose given at one single time may give of more damage to normal surrounding tissues

Protraction

refers to the overall length of time over which radiation therapy is delivered, from the first fraction to the last fraction

Protraction

Giving radiation longer than intended may help normal tissue to recover; however, cancer can also reproduce

5 R’s

explain why radiation works and how tumor and normal tissues respond differently to radiation

5 R’s

They are essential for understanding treatment planning, dose schedules, and expected outcomes

REPAIR

-the process of rejoining DNA strands.

15 minutes to 1 hour

Most repairs occur within ____ to _____

REOXYGENATION

occurs as the sensitive, well-oxygenated tumor cells are killed and the tumor shrinks

REPOPULATION

the ability of the cell population to continue to divide and to replace dying and dead cells

REDISTRIBUTION

reflects the variability of a cell’s radiosensitivity over the cell cycle

REDISTRIBUTION

-Cells in different parts of the reproductive cycle have different sensitivities

M

is the most sensitive, and late S is the least sensitive

M phase

S phase

Radiation exposure kills more of the cells in the ___, and more cells in the ___survive