Week 2- Effects of Radiation Exposure

Define Radiobiology

Studies the biological effects of ionizing radiation on living organisms

Direct vs Indirect Radiation

• Direct = 1/3 of ionizing radiation

• Indirect = 2/3 of ionizing radiation → MORE COMMON

What happens when biological material is irradiated?

DNA is damaged

Why is radiolysis of water the first step in the primary mechanism of biological damage to macromolecules? Indirect or direct?

Ionization causes particles in water to split causing free radicals such as those in hydroxyl and hydrogen

• Indirect effect

Deterministic vs. Stochastic Effects of Radiation

• Deterministic: manifest only after radiation exceeds a certain threshold

• Stochastic: random, no threshold

Law of Bergonie and Tribondeau

• The younger (stem) the cell the more radiosensitive, the older, the less radiosensitive

• More proliferative = more radiosensitive

• More metabolic activity = more radiosensitive

Tissues with High resistance to radiation vs tisues with low resistance to radiation

High resistance: optical lens, muscles and nerves

Low: Lymphoid, bone marrow, testes, Intestines, Mucous membranes

Radiation Early effects vs. Late effects

Early: occur right after irradiation, 3-4 months

Late: occur from 6 monthd-years

4 Stages of Acute Radiation Syndrome

• Prodromal period: nausea, vomiting, diarrhea = earliest clinical symptoms

• Latent: patient looks and feels ok

• Manifest illness

• Recovery or Death

Different dosages relating to syndromes

>200 -1000 rad = hematologic syndromes

>1000-5000 rad = gastrointestinal syndromes

>5000 = central nervous system syndromes

Therapeutic effects of radiation can cause other problems in the oral cavity, what are they (5)

• Developmental

• Acquired

  • Mucositis: death of basal cells causes focal hyperemia and edema

    

  • Candidiasis: fungal infection, decrease WBC count, causes loss of tissue

    

  • Xerostomia: salivary glands get affected by radiation (parotid most sensitive) which leads to reduced or thickening of saliva, causes dryness, burning, cracked lips, mouth, tongue change

    • Treat with artificial saliva and sialogues, control caries, avoid sugary and spicy foods

  

  • Radiation caries: Decrease in saliva and demineralization along with heavy plaque causes caries. Can also cause effects to fetus

    

  • Osteoradionecrosis: Bone becomes exposed after oral radiation

    • Stochastic effect: only appear when exposed to >50Gy

    • More common in mandible

    • 3Hs: Hypovascularity, Hypocellularity, Hypoxia (local)

    • Pain, swelling, drainage

      

Radiation Effects on Embryo/Fetus

• 2 Weeks

• 3-8 Week

• 9 Weeks-birth

• 2 Weeks: embryonic death and miscarriage

• 3-8 Week: congenital malformations, miscarriage

• 9 Weeks-birth: mental retardation, microcephaly, stunting growth

What is the lowest level of radiation that can be lethal for young fetus?

What level of radiation will cause mental retardation at 8-15 weeks?

• >0.1 grays (Gy) can be a lethal dose or damage threshold

• 0.5 grays (Gy)

Define teratogen

An agent that causes congenital birth defects

Can you take x-rays on pregnant women?

Yes, with proper precautionary measures