Rad bio test 3 cell survival curve indepth

Who are Puck and Marcus?

Irradiated human cervical (HeLa) cells in a Petri dish and led to the development of cell survival curves

What did Puck and Marcus contribute to radiation biology?

Cell survival curves

What are the three outcomes observed when a cell population is irradiated?

Lethal damage, sublethal damage, or no damage

What happens to cells that are lethally damaged?

All targets are hit and the cell dies

What happens to cells that are sublethally damaged?

A few targets are hit and the cell may repair damage

What happens to cells with no damage?

No targets are hit and the cell survives

What happens as radiation dose increases?

The probability of cellular targets being hit increases

What is the Law of Bergonie and Tribondeau?

Ionizing radiation is more effective against actively mitotic, undifferentiated cells with a long mitotic future

Which cells are most radiosensitive according to Bergonie and Tribondeau?

Actively dividing, undifferentiated cells with long mitotic future

What does enhanced response to radiation indicate?

Radiosensitivity

What does diminished response to radiation indicate?

Radioresistance

What are the three groups of factors influencing radiation response?

Physical, chemical, and biologic factors

What do these factors affect?

Cellular radioresponse and the shape of survival curves

What happens to the shoulder region (Dq) with high LET radiation?

It decreases or may be absent

How do survival curves appear with high LET radiation?

Steeper (lower Do)

Why does LET affect biologic response?

Due to differences in energy deposition density in the cell

What is the second physical factor influencing radioresponse?

Dose rate

When is dose rate effect significant?

With low LET radiation (x-rays and gamma rays)

Is dose rate effect seen with high LET radiation?

No

What are the two types of chemical factors affecting radiation response?

Radiosensitizers and radioprotectors

What do radiosensitizers do?

Enhance radiation response

What do radioprotectors do?

Decrease radiation response

What is the most potent radiosensitizer?

Oxygen

When must oxygen be present to be effective?

During radiation exposure

When is oxygen effect most significant?

With low LET radiation

What happens as oxygen levels decrease?

Cell response decreases and survival curve shifts right

What happens to Dq and Do when oxygen decreases?

They increase

With what radiation types is oxygen effect most pronounced?

X-rays and gamma rays

What is the Oxygen Enhancement Ratio (OER)?

Ratio of radiation dose under hypoxic conditions to dose under oxic conditions for the same effect

What is the typical OER for x-rays and gamma rays?

2.5 to 3.0

How much more resistant are hypoxic cells?

2.5 to 3 times more resistant than oxic cells

what is the most important group of radioprotectors?

Sulfhydryls (free sulfur compounds)

When must radioprotectors be present?

During irradiation

When are radioprotectors usually given?

30 minutes before exposure

With which radiation are sulfhydryls most effective?

Low LET radiation

What are the two main biological factors influencing radiation response?

Cell cycle position and ability to repair sublethal damage

When are cells most radiosensitive in the cell cycle?

G2 and M phases

When do cells have intermediate sensitivity?

G1 phase

When are cells most radioresistant?

S phase (especially late S)

What happens to cell survival when radiation is given in fractions?

Cell survival increases

Why does fractionation spare normal tissue?

Allows repair of sublethal damage in normal cells

How does hypoxia affect repair?

Reduces ability to repair sublethal damage

Why is tumor response favorable with fractionation?

Hypoxic tumor cells repair less effectively

How long does sublethal damage repair take after low LET radiation?

Several hours depending on dose per fraction