Rad bio test 3 cell survival curves

Who conducted experiments that led to cell survival curves?

Puck and Marcus

What type of cells did Puck and Marcus irradiate?

HeLa (human cervical) cells

Where were the cells irradiated in Puck and Marcus experiments?

Petri dish

What are the three possible outcomes when cells are irradiated?

Lethally damaged, sublethally damaged, or no damage

What happens to target hits as radiation dose increases?

Probability of targets being hit increases

What does the Law of Bergonie and Tribondeau state?

Radiation is more effective on actively dividing, undifferentiated cells with a long mitotic future

Which cells are most radiosensitive according to Bergonie and Tribondeau?

Actively mitotic, undifferentiated cells

What are the three categories of factors influencing radiation response?

Physical, chemical, biologic

What do radiosensitive cells exhibit?

Enhanced response to radiation

What do radioresistant cells exhibit?

Diminished response to radiation

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

Decreases or disappears

How does high-LET radiation affect the survival curve slope?

Makes it steeper (lower Do)

Why does LET affect biologic response?

Differences in energy deposition density

What is the second major physical factor affecting radiation response?

Dose rate

When is dose rate effect significant?

Low-LET radiation

Is dose rate effect seen with high-LET radiation?

No

What are radiosensitizers?

Agents that increase radiation effect

What are radioprotectors?

Agents that decrease radiation effect

What is the most potent radiosensitizer?

Oxygen

When must oxygen be present to be effective?

During radiation exposure

With which type of radiation is oxygen effect most significant?

Low-LET radiation

What happens to the survival curve as oxygen decreases?

Shifts right (increased Dq and Do)

What does a right shift in survival curve indicate?

Increased radioresistance

What is the Oxygen Enhancement Ratio (OER)?

Dose under hypoxic conditions divided by dose under oxic conditions for same effect

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

2.5 to 3.0

What does an OER of 2.5–3.0 indicate?

Hypoxic cells are 2.5–3x more resistant

What is the most important group of radioprotectors?

Sulfhydryls

When are radioprotectors typically administered?

30 minutes before radiation

When must radioprotectors be present?

During irradiation

With which radiation are sulfhydryls most effective?

Low-LET

What biological factors influence radiation response?

Cell cycle position and repair ability

Which phase is most radiosensitive?

G2 and M

Which phase has intermediate sensitivity?

G1

Which phase is most radioresistant?

S phase (especially late S)

How does fractionation affect cell survival?

Increases survival compared to single dose

Why does fractionation spare normal tissue?

Allows repair of sublethal damage

How does hypoxia affect repair of sublethal damage?

Reduces repair capacity

Why does hypoxia improve tumor response with fractionation?

Tumor cells repair less effectively

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

Several hours