Radiation Effects on Human Health

Study Notes

Radiation effects can be categorized into three types: sub-acute, acute, and chronic, each with different severity and characteristics.

Occur within weeks to a few months after exposure
Include hematopoietic syndrome (damage to bone marrow, leading to decreased blood cell production) and gastrointestinal syndrome (damage to the lining of the gastrointestinal tract, leading to nausea, vomiting, diarrhea, and severe dehydration)

Occur within hours to days of exposure to high levels of radiation
Severity depends on the dose received:
- Mild Exposure (1-2 Gy): Nausea, vomiting, and fatigue
- Moderate Exposure (2-6 Gy): More severe nausea and vomiting, hair loss, and damage to the bone marrow leading to infections and bleeding
- Severe Exposure (6-10 Gy): Severe gastrointestinal symptoms, significant bone marrow damage, and a high risk of infections and bleeding; without medical treatment, survival is unlikely
- Very High Exposure (above 10 Gy): Severe damage to internal organs and tissues, often resulting in death within days to weeks

Emerge months to years after exposure and can result from lower doses of radiation over extended periods
Include:
- Cancer: Increased risk of various types of cancer due to DNA damage and mutations
- Cataracts: Radiation-induced damage to the lens of the eye, leading to clouding and vision impairment
- Cardiovascular Diseases: Increased risk of heart disease and stroke due to damage to blood vessels and heart tissues
- Fibrosis: Tissue scarring and loss of function in organs such as the lungs and liver

Radiation therapy targets cancer cells by damaging their DNA, disrupting their ability to replicate and survive
Key factors include:
- DNA Damage and Repair: Radiation causes breaks in DNA strands
- Cell Cycle Sensitivity: Cells are most sensitive to radiation during certain phases of the cell cycle
- Hypoxia: Tumor cells in low-oxygen environments are more resistant to radiation
- Fractionation: Delivering radiation in smaller, multiple doses allows normal cells time to repair between treatments

Measures the balance between the therapeutic effect of a treatment and its toxic side effects
Includes:
- Enhanced Efficacy: Drugs can enhance the effect of radiation on tumor cells
- Radio Protectors: Some agents can protect normal tissues from radiation damage
- Radio Sensitizers: Drugs that make cancer cells more sensitive to radiation
- Synergistic Effects: The combination of radiation and drugs can have a greater effect than either treatment alone

The likelihood that a given treatment regimen will completely eradicate a tumor
Factors affecting TCP include:
- Dose-Response Relationship: TCP increases with higher doses of radiation
- Heterogeneity: Tumor cells can vary widely in their sensitivity to radiation
- Hypoxia: Hypoxic tumor cells are more resistant to radiation
- Biomarkers: Identifying biomarkers that predict tumor response to radiation can help personalize treatment

Estimates the risk of damage to healthy tissues from radiation therapy
Factors affecting NTCP include:
- Dose Constraints: Limits are set on the maximum dose that normal tissues can receive
- Volume Effects: The amount of normal tissue exposed to radiation affects NTCP
- Fractionation: Spreading the total radiation dose over several sessions reduces the risk to normal tissues
- Individual Sensitivity: Genetic differences can affect how patients react to radiation