Radiosensitivity & Cell Age in Mitotic Cycle

Question 1

When are cells most radiosensitive?

Answer 1

When they are close to mitosis

Question 2

When are cells most radioresistant?

Answer 2

In the latter part of s-phase

Question 3

Radiosensitivity in G1 phase

Answer 3

Resistant early followed by sensitivity later

Question 4

Radiosensitivity in G2 and M phases

Answer 4

Are equally sensitive

Question 5

Checkpoint Genes

Answer 5

Halt cells at G2 phase to inventory and repair damage before mitosis

Question 6

Cells where checkpoint gene is inactivated

Answer 6

Move directly to mitosis without repairing any damage and are more sensitive to UV and ionizing radiation

Question 7

Total Cell Cycle Time

Answer 7

11-24 hours

Question 8

Time of mitosis

Answer 8

1 hour

Question 9

Time of s-phase

Answer 9

6-8 hours, never exceeds 18 hours

Question 10

Time of G1 phase

Answer 10

1-11 hours

Question 11

Time of G2 phase

Answer 11

3-4 hours

Question 12

Oxygen Enhancement Ratio (OER)

Answer 12

Aerated cells are more radiosensitive due to oxygen reacting with free radicals to produce peroxide which constitutes non-repairable damage.

Typical values are 2.5-3 for gamma and x-rays