5. Radiation Biology

Question 1

What are the objectives of radiation biology?

Answer 1

Understanding X-ray interaction with biological molecules, stochastic and deterministic effects, and effects of therapeutic radiation.

Question 2

What principle should be followed to minimize radiation risks?

Answer 2

The ALARA principle: ‘As Low As Reasonably Achievable’.

Question 3

What happens to low-energy X-rays in the body?

Answer 3

They are completely absorbed, typically by hard tissues like bone and teeth.

Question 4

What happens to high-energy X-rays in the body?

Answer 4

They undergo Compton scattering, releasing secondary electrons that damage DNA.

Question 5

What is the difference between direct and indirect radiation damage?

Answer 5

Direct: Photon interacts directly with molecules. Indirect: Secondary electrons create radicals from water.

Question 6

What are free radicals and how are they generated?

Answer 6

Highly reactive molecules with unpaired electrons, generated within 10^-10 seconds after photon passage.

Question 7

When are cells most sensitive to radiation?

Answer 7

In the G2 and M phases; least sensitive in the S phase.

Question 8

What happens to DNA before and after chromosomal duplication when damaged by radiation?

Answer 8

Before duplication: Chromosome aberrations. After duplication: Chromatid aberrations.

Question 9

What are stochastic effects of radiation?

Answer 9

Include genetic mutations and somatic mutations, increasing risk with dose.

Question 10

What are deterministic effects of radiation?

Answer 10

Includes cell death, bystander effects, and apoptosis.

Question 11

What does the Law of Bergonie and Tribondeau state about radiosensitivity?

Answer 11

Radiosensitivity is greatest in cells with high mitotic activity, long mitotic future, and undifferentiated cells.

Question 12

What is acute radiation syndrome and its stages?

Answer 12

A syndrome from whole-body doses, with stages like prodromal (nausea), hematopoietic (infection), and CNS (death).

Question 13

What are the somatic effects of low radiation doses?

Answer 13

Cataracts form at 0.5 Gy; risks for mental retardation and childhood cancer increase with exposure.

Question 14

What are the fetal effects of radiation exposure at different developmental stages?

Answer 14

Preimplantation: lethal effects at 100 mGy. Organogenesis: risks like microcephaly. Late fetal period: cancer risk.

Question 15

How does fractionation of radiation doses reduce damage?

Answer 15

Spreading radiation doses over time to reduce overall damage.

Question 16

What are the benefits of fractionation in radiation therapy?

Answer 16

Includes cellular repair, tumor reoxygenation, and repositioning tumor cells into radiosensitive phases.

Question 17

What is the typical radiation dose in oral radiotherapy?

Answer 17

2 Gy daily for 6-7 weeks, totaling 60-70 Gy.

Question 18

What is intensity-modulated radiotherapy (IMRT)?

Answer 18

A technique to control dose distribution in radiotherapy.

Question 19

What are the effects of therapeutic radiation on the oral cavity?

Answer 19

Includes xerostomia, radiation caries, and osteoradionecrosis.

Question 20

What is osteoradionecrosis, and when is the risk highest?

Answer 20

Bone damage from radiation, with highest risk 4-12 months post-therapy.

Question 21

What causes radiation caries?

Answer 21

Reduced saliva flow and changes in composition due to radiation.

Question 22

How does radiation affect salivary glands?

Answer 22

Reduces salivary flow, damaging acinar cells; parotid glands have a dose limit of 25 Gy.

Question 23

Does radiation affect mature teeth and bone?

Answer 23

No effect on mature teeth; damages tooth buds and bone at doses of 60-70 Gy.

Question 24

What is trismus and its cause in radiation therapy?

Answer 24

Reduced jaw opening due to muscle inflammation and fibrosis.