Radiobiology

Question 1

What is radiobiology?

Answer 1

Radiobiology is the study of the sequence of events after the absorption of energy from ionizing radiation, the organism’s response, and the resulting damage.

Question 2

What is ionizing radiation?

Answer 2

Ionizing radiation excites atoms to the point of ejecting electrons, creating charged particles (ions), which can damage cells either directly or indirectly.

Question 3

What are direct and indirect ionizations?

Answer 3

Direct ionization: Charged particles (like alpha particles) directly damage DNA.

Indirect ionization: Radiation produces free radicals, primarily from water, that cause secondary damage to cells.

Question 4

What is radiolysis of water?

Answer 4

Radiolysis is the splitting of water molecules by radiation, creating free radicals like hydroxyl radicals and hydrogen peroxide, which are toxic to cells.

Question 5

What is Linear Energy Transfer (LET)?

Answer 5

LET measures the energy transferred by ionizing radiation as it travels through tissue. High LET radiation (alpha particles) causes more damage than low LET (x-rays, gamma rays).

Question 6

What is Relative Biological Effectiveness (RBE)?

Answer 6

RBE compares the biological effectiveness of different types of radiation at producing the same biological effect. As LET increases, RBE also increases.

Question 7

What is the Oxygen Enhancement Ratio (OER)?

Answer 7

OER compares radiation effects in the presence of oxygen versus in anoxic conditions. Cells in oxygen-rich environments are more radiosensitive.

Question 8

What is the most lethal type of DNA damage caused by radiation?

Answer 8

Double-strand breaks are the most lethal form of DNA damage because they are difficult for the cell to repair.

Question 9

What are the four types of radiation-induced DNA damage?

Answer 9

Base damage

Single-strand breaks

Double-strand breaks

Cross-linking (abnormal bonds between DNA strands or proteins).

Question 10

What is the Law of Bergonie and Tribondeau?

Answer 10

Ionizing radiation is most effective against cells that are actively dividing, undifferentiated, and have a long mitotic future.

Question 11

What are examples of radiosensitive and radioresistant cells?

Answer 11

Radiosensitive: Basal cells, crypt cells, erythroblasts.

Radioresistant: Nerve cells, muscle cells.

Question 12

What factors affect a cell’s response to radiation?

Answer 12

Physical factors: LET, dose rate.

Chemical factors: Radiosensitizers and radioprotectors.

Biological factors: Cell cycle phase and ability to repair damage.

Question 13

How does hypoxia affect radiation treatment?

Answer 13

Hypoxic (low-oxygen) tumor cells are 2-3 times more resistant to radiation because oxygen enhances the effects of radiation by forming DNA-damaging free radicals.

Question 14

What is fractionation in radiation therapy?

Answer 14

Fractionation refers to delivering radiation in small daily doses to allow normal tissues to repair between treatments while still targeting the tumor.

Isoeffect curves are most closely associated fractionation.

Question 15

What are the four R’s of radiobiology?

Answer 15

1. Repopulation: Tissue regrows during treatment.
2. Redistribution: Cells move into more radiosensitive phases of the cell cycle.
3. Repair: Normal tissues repair sublethal damage (radiation damage to a cell that is not sufficient to kill the cell).
4. Reoxygenation: Tumor cells gain oxygen and become more radiosensitive between doses.

Question 16

Which macromolecule is most radiosensitive?

Answer 16

Deoxyribonucleic acid (DNA)

Question 17

Fractionation of radiation dose administration to neoplastic tissues has the the following effects.

Answer 17

Reoxygenation of hypoxic tumor cells, thus promotes their sensitivity to subsequent doses.

Favors repair of radiation injury in normal cells over that of cancer cells.

Reduces or blunts the effects of the radiation injury in early responding normal tissues.

Question 18

The tolerance dose TD 50/5 for the lens of the eye is __________ to/than the TD 5/5 for the lens of the eye.

Answer 18

GREATER

TD 5/5: This is the dose that would cause a complication (like cataracts) in 5% of patients within 5 years.

TD 50/5: This is the dose that would cause a complication in 50% of patients within 5 years.

The TD 50/5 dose is higher because it reflects a dose level where complications are more likely, affecting 50% of patients instead of just 5%.

Question 19

What does the term interphase death mean?

Answer 19

The cell dies prior to leaving interphase.