RT206 SYSTEMIC BODY RESPONSE HANDOUT

Systemic response

Biological response occurring when radiation damages actively dividing and undifferentiated cells

1. Total radiation dose

2. Dose rate

3. Type of radiation

4. Tissue radiosensitivity

Factors determining the severity of systemic radiation response

Early Effects (Acute Effects)

Radiation effects occurring within hours to weeks of exposure

Late Effects (Chronic Effects)

Radiation effects occurring months to years after exposure

Direct effect

Ionization of DNA resulting in strand breaks and mutations

Indirect effect

Radiolysis of water leading to the formation of free radicals

1. Rapidly dividing

2. Poorly differentiated

3. Highly metabolic

Characteristics of radiosensitive cells

Law of Bergonie and Tribondeau

Scientific principle stating that radiosensitivity is higher in rapidly dividing, poorly differentiated, and highly metabolic cells

1. Bone marrow

2. Gastrointestinal lining

3. Reproductive organs

Highly affected tissues primarily associated with systemic effects

Deterministic Effects (Tissue Reactions)

Synonyms for Early Effects

1. Occur shortly after exposure

2. Dose-dependent severity

3. Threshold dose

Key characteristics of Early Effects (Deterministic Effects)

Acute Radiation Syndrome (ARS)

Condition caused by high-dose, whole-body exposure affecting rapidly dividing cells in the bone marrow, GI, and CNS systems

Stochastic Effects

Synonyms for Late Effects

1. Occur months to years after exposure

2. Probability-based

3. No threshold dose

Key characteristics of Late Effects (Stochastic Effects)

1. Cancer

2. Genetic mutations

Common examples of Late Effects (Stochastic Effects)

1. Bone marrow 2. Circulating blood 3. Spleen 4. Thymus 5. Lymphatic tissues

Primary components of the hematologic/hemopoietic system

Parenchyma

Functional tissue of bone marrow containing stem cells and fat cells

Stroma

Support tissue providing structural support to the bone marrow

Red Bone Marrow

Type of bone marrow responsible for producing RBCs, WBCs, and platelets

1. Ribs

2. Vertebrae

3. Sternum

4. Skull

5. Ends of long bones

Anatomical locations of red bone marrow

Fatty marrow

Synonyms for Yellow Bone Marrow

Fat cells

Composition of yellow bone marrow

Decrease in hematopoietic stem cells

Primary radiation effect on the hematologic system

Slight decrease in stem cells with rapid recovery

Hematologic effect of a low radiation dose

Significant depletion of stem cells with delayed recovery

Hematologic effect of a moderate radiation dose

Severe depletion of stem cells with incomplete or no recovery

Hematologic effect of a high radiation dose

Erythroblasts

Radiosensitive RBC precursor cells

Myelocytes

Moderately sensitive WBC precursor cells

Megakaryocytes

Least sensitive platelet precursor cells

Anemia

Result of decreased Red Blood Cells (RBCs)

Infection risk

Result of decreased White Blood Cells (WBCs)

Bleeding

Result of decreased Platelets

Lymphocytes

Blood cells first to decrease following radiation exposure

10 rads (100 mGy)

Radiation dose at which lymphocytes begin to decrease

Neutrophils

Blood cells that decrease at around 50 rads (500 mGy) and reach lowest levels within 1 week

Platelets and Red Blood Cells

Blood cells affected at doses greater than 50 rads with a slower response due to long lifespan

4 weeks

Estimated time for recovery of platelets and RBCs post-exposure

Fat and fibrous tissue

Tissue replacement seen in bone marrow after high doses of radiation

Epidermis

Radiosensitive basal cell layer of the skin

Basal cells

Actively dividing, immature cells in the epidermis responsible for continuous regeneration

2%

Daily replacement percentage of skin cells

Dermis

Skin layer composed of connective tissue containing hair follicles and sweat glands

1. Hair follicles

2. Sebaceous glands

3. Sweat glands

4. Sensory receptors

Accessory structures located within the dermis

Subcutaneous layer

Skin layer providing insulation and protection containing fat and connective tissue

Skin Erythema

Skin redness caused by capillary dilation within 1–2 days of exposure to 100–1000 rad

SED 50 ​≈ 600 rad (6 Gy)

IT IS SED WITH (LOWER CASE 50)

Radiation dose causing erythema in 50% of individuals

Desquamation

Peeling of the skin due to basal cell damage

Dry desquamation

Mild peeling of the skin

Moist desquamation

Severe skin peeling accompanied by fluid exudation

Epilation

Synonyms for hair loss

1. Atrophy

2. Fibrosis

3. Pigmentation changes

4. Ulceration

5. Necrosis

6. Skin cancer

Late effects of high radiation doses on the skin

Atrophy

Thinning of the skin

Fibrosis

Hardening of skin due to connective tissue growth

Necrosis

Tissue death

Temporary hair loss (epilation)

Effect of a moderate radiation dose on highly radiosensitive hair follicles

Permanent hair loss

Effect of a high radiation dose on hair follicles

1. Atrophy

2. Fibrosis

3. Reduced or absent function

Effects of high radiation doses on sweat and sebaceous glands

1. Thickened skin

2. Discoloration

3. Tight, brittle texture

4. Cracking and flaking

Nonmalignant skin changes caused by chronic or repeated radiation exposure

Rapid epithelial turnover

Reason for high radiosensitivity of the digestive system

1. Oral mucosa

2. Esophagus

3. Stomach

4. Intestines

Principal areas of the digestive system affected by radiation

Week 1

Mucositis progression stage involving mild erythema and edema

Week 2

Mucositis progression stage involving pain, taste alteration, and patchy mucositis

Week 3

Mucositis progression stage involving severe mucositis and difficulty swallowing

Dysphagia

Term for difficulty swallowing

Week 4

Mucositis progression stage involving confluent mucositis and tissue sloughing

Week 5

Mucositis progression stage involving peak damage and extreme sensitivity

2–4 weeks

Timeline for recovery of digestive mucosa after therapy

Xerostomia

Term for dry mouth due to salivary gland damage

1. Esophagitis

2. Odynophagia

3. Burning sensation

Acute effects of radiation on the esophagus

Odynophagia

Term for painful swallowing

1. Fibrosis

2. Ulceration

3. Difficulty swallowing

Late effects of radiation on the esophagus

10–12 days

Typical time of appearance for esophageal radiation symptoms

Short-lived surface cells

Radiosensitive cells of the stomach

Long-lived glandular cells

Radioresistant cells of the stomach

1. Nausea and vomiting

2. Delayed gastric emptying

3. Epithelial denudation

Early effects of radiation on the stomach

Epithelial denudation

Loss of the stomach's mucosal lining

1. Gastritis

2. Peptic ulceration

3. Fibrosis

Late effects of radiation on the stomach

>40 Gy

Radiation dose required for peptic ulceration

crypts of Lieberkühn

Site of stem cells in the highly radiosensitive small and large intestines

1. Villi atrophy

2. Epithelial loss

Early intestinal effects occurring within 2–4 days

1. Diarrhea

2. Abdominal pain

Primary early symptoms of intestinal radiation damage

1. Fibrosis

2. Ischemia

3. Stenosis

4. Adhesion formation

5. Obstruction

Late effects of radiation on the intestines

Ischemia

Reduced blood supply to tissues

Stenosis

Narrowing of the intestinal lumen

1. Basal layer

2. Intermediate layers

3. Surface layer

Layers of the bladder lining

Basal cells

Small, actively dividing diploid cells in the bladder lining

Surface cells

Large polyploid cells with thick membranes that protect underlying bladder tissue

Low cell turnover rate

Reason the bladder is considered relatively radioresistant in early stages

1. Increased frequency

2. Urgency and discomfort

3. Irritation

Early or intermediate effects of radiation on the bladder

1. Fibrosis

2. Reduced capacity

3. Radiation cystitis

Late effects of radiation on the bladder

Radiation cystitis

Chronic urinary dysfunction resulting from bladder wall damage

Moderately radiosensitive (late-responding)

Radiosensitivity classification of kidneys

Nephron

Functional unit of the kidney that is sensitive to radiation

1. Radiation nephropathy

2. Glomerular injury

3. Tubular damage

4. Vascular damage

Late radiation effects on kidneys occurring months to years post-exposure

1. Hypertension

2. Proteinuria

3. Decreased GFR

4. Renal insufficiency

Clinical manifestations of kidney radiation damage

Proteinuria

Condition of having protein in the urine

Intermediate to late-responding

Radiosensitivity response classification of the respiratory system

Radiation pneumonitis

Early phase lung effect occurring 2–6 months post-exposure

1. Cough

2. Dyspnea

3. Chest discomfort

Symptoms of radiation pneumonitis

Pulmonary fibrosis

Late phase lung effect characterized by scarring and impaired gas exchange