Injury Produced by Ionizing Radiation

Slide 1 · Injury Produced by

Ionizing Radiation

From ionization to tissue injury, fibrosis, and carcinogenesis

Energy deposition

DNA / vascular injury

Clinical sequelae

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Distinguish ionizing from nonionizing radiation and describe common radiation types.

Explain how radiation damages DNA and why proliferating tissues are vulnerable.

Recognize acute systemic effects, delayed vascular injury, and radiation-induced fibrosis.

Connect imperfect DNA repair to mutagenesis and later malignancy.

Slide 3 · Why ionizing radiation is a pathology problem

Radiation has indispensable diagnostic and therapeutic applications.

The same energy deposition can cause tissue loss, chronic scarring, and genetic injury.

Consequences depend on radiation properties, tissue susceptibility, field size, and timing.

Pathology includes both direct cellular changes and delayed vascular–stromal remodeling.

Slide 4 · Radiation: Energy transferred to matter

Radiation may travel as waves or energetic particles.

Biologic effects depend on whether energy can eject bound electrons.

Ionization changes molecular chemistry and can initiate tissue injury.

Nonionizing

Ionizing

Insufficient energy to displace tightly bound electrons

Can remove electrons from atoms

Different physical interactions; Different biological consequences

Slide 5 · Ionizing versus nonionizing energy

Nonionizing energy is insufficient to remove tightly bound electrons.

Ionizing radiation liberates electrons from atoms or molecules.

Do not equate every radiation modality with ionization.

Nonionizing

Ionizing

Insufficient energy to displace tightly bound electrons

Can remove electrons from atoms

Different physical interactions; Different biological consequences

Slide 6 · What produces ionizing radiation?

X-rays and gamma rays are high-energy electromagnetic radiation.

Alpha and beta particles are particulate radiation.

High-energy neutrons also cause ionizing injury.

X-rays / γ-rays

High-energy photons

α particles

2 protons + 2 neutrons

β particles

Electron or positron

Neutrons

Uncharged particles

Slide 7 · X-rays and gamma rays: Distributed deposition

Both are high-energy photons capable of ionization.

They travel farther in tissue than densely ionizing alpha particles in the source comparison.

At equivalent energy, damage is distributed over a deeper or longer track.

Medical diagnostic imaging and radiotherapy exploit photon radiation.

Slide 8 · Alpha particles: Concentrated tissue injury

Alpha particles contain two protons and two neutrons.

They transfer substantial energy across a restricted region.

The local biologic effect differs from that of sparsely ionizing photons.

Internal deposition of alpha-emitting material is relevant to radon-associated lung risk.

Slide 9 · Beta particles and neutrons

Beta particles consist of electrons or positrons.

Neutrons are another type of high-energy ionizing radiation.

Particle identity influences how physical energy is deposited in tissues.

Equal absorbed energy does not guarantee equal biological effect.

Slide 10 · Spatial pattern of ionization matters

Dense localized ionization can severely damage a restricted region.

More distributed deposition may expose deeper tissues.

Compare both absorbed dose and radiation quality when interpreting effects.

Same incident energy does not imply the same spatial injury pattern

α: Concentrated deposition

X/γ: More dispersed path

Slide 11 · Sources of exposure in medical practice

Diagnostic imaging exposes tissues to ionizing radiation.

Cancer radiotherapy deliberately directs radiation at target volumes.

Diagnostic and therapeutic radioisotopes are additional medical sources.

Clinical benefit must be interpreted alongside potential acute and late effects.

Slide 12 · Radiation is a therapeutic double-edged sword

Ionizing energy can arrest proliferation and kill target cells.

Surrounding normal tissues may accumulate acute or delayed lesions.

Radiotherapy aims for tumor effect with acceptable normal-tissue injury.

Ionizing radiation

Tumor-cell injury

Normal-tissue injury

Clinical benefit depends on control of normal-tissue effects

Schematic

Slide 13 · Three distinct ways to describe a dose

Source activity, absorbed energy, and biologically weighted dose describe different concepts.

The units Ci, Gy, and Sv therefore answer different questions.

Do not substitute one unit for another without specifying the quantity.

Activity

Radionuclide disintegrations

Ci

Absorbed dose

Energy per mass

Gy

Equivalent/effective dose

Biologic weighting

Sv

Slide 14 · Curie: Activity of a radioactive source

The curie (Ci) describes radionuclide disintegrations per second.

It quantifies activity of a source, not energy absorbed by a target.

Two sources with the same activity need not deliver the same tissue dose.

Slide 15 · Gray: Energy absorbed per tissue mass

The gray (Gy) measures absorbed radiation dose.

The unit reflects energy delivered to a mass of irradiated material.

Absorbed dose is not by itself a complete measure of biologic harm.

Slide 16 · Sievert: Biologically weighted radiation dose

The sievert (Sv) expresses equivalent or effective dose after biological weighting.

For the same absorbed dose, radiation qualities can produce different injury.

Interpret Sv in the context of the quantity being reported and exposure geometry.

Slide 17 · Radiation units: Diagnostic distinctions

Quantity

Unit

What it represents

Radioactivity

Curie (Ci)

Nuclear disintegration rate

Absorbed dose

Gray (Gy)

Energy absorbed per unit mass

Equivalent / effective dose

Sievert (Sv)

Biologically weighted radiation dose

Radiation weighting and tissue distribution affect interpretation; These are not interchangeable quantities.

Slide 18 · Biologic injury has multiple determinants

Radiation quality and total absorbed dose influence the primary lesion.

Dose rate and fractionation determine opportunities for repair.

Exposed field size controls how much functional tissue is threatened.

Cell proliferation, oxygenation, and vascular integrity modify outcomes.

Slide 19 · Dose fractionation permits partial repair

Dividing an exposure into fractions permits repair of some sublethal damage.

Cumulative harm depends on residual injury after each interval.

Normal-tissue recovery underpins the therapeutic use of fractionation.

First exposure

Repair interval

Next exposure

Schematic

Slide 20 · Why fractionated radiotherapy can work

Tumor and normal cells may differ in capacity for repair and recovery.

Intervals between treatments allow some normal tissues to recover.

Tumor killing can accumulate when damage is inadequately repaired.

Fractionation does not eliminate late toxicity or make irradiation harmless.

Slide 21 · Field size modifies the clinical consequence

A restricted field can receive a high dose without exposing the whole body.

A larger field injures more critical tissues and stem-cell compartments.

The same nominal dose may have different consequences in focal versus whole-body exposure.

Small field

Large field

Local tissue exposure

More tissues affected

Slide 22 · Cell proliferation predicts radiosensitivity

Ionizing radiation injures DNA needed for successful cell division.

Rapidly proliferating cell populations express injury early.

Bone marrow, lymphoid tissue, germ cells, and GI mucosa are vulnerable.

Bone marrow

Rapid turnover

Lymphoid tissue

Highly sensitive

GI mucosa

Rapid renewal

Germinal cells

Proliferative

Slide 23 · High-turnover tissue: Why injury appears early

Stem and progenitor cells are required for continual tissue replacement.

Their depletion first becomes apparent as short-lived mature cells are lost.

Damaged proliferative compartments may recover if viable precursors remain.

Severe depletion prevents tissue reconstitution and prolongs dysfunction.

Slide 24 · Quiescent cells are relatively radioresistant

Nondividing neurons and mature muscle cells are less vulnerable to division-dependent DNA injury.

Extremely high doses may interfere with essential nuclear functions in such cells.

Relative cellular resistance does not protect an organ from vascular or stromal injury.

Slide 25 · Oxygen modifies free-radical injury

Radiolysis of water yields reactive species that injure DNA.

Oxygen enhances the effectiveness of radical-mediated damage.

Hypoxic tissue, including poorly perfused tumor regions, is less sensitive to this pathway.

Radiation + water

Free radicals

Oxygen-rich

Hypoxic

More effective radical-mediated DNA damage

Reduced sensitivity to indirect damage

Slide 26 · Hypoxic tumor regions: Mechanistic implication

Rapid tumor growth can outstrip local vascular supply.

Low oxygen tension reduces indirect radiation injury.

Consequently, nonhypoxic tumor areas may respond differently from hypoxic areas.

Oxygen effect is a biologic modifier, not a substitute for dosimetry.

Slide 27 · Two pathways converge on DNA damage

A direct effect transfers energy to DNA or other macromolecules.

An indirect effect produces free radicals, particularly from water.

Free-radical production as a major mechanism.

Ionizing radiation

Direct DNA interaction

Water radiolysis → radicals

Either route can produce DNA lesions

Schematic

Slide 28 · Indirect damage begins with radiolysis

Biological tissues contain abundant water.

Radiolysis generates highly reactive chemical intermediates.

These species can alter DNA even when radiation does not strike the DNA directly.

Radiation energy

Water radiolysis

Reactive radicals / ROS

DNA injury

Schematic

Slide 29 · DNA injury has several molecular forms

Reported lesions include base changes, single-strand breaks, and DNA–protein crosslinks.

Double-strand breaks are particularly consequential for genomic integrity.

Different lesions differ in repair complexity and consequences.

Base lesions

Strand breaks

Crosslinks

Schematic

Slide 30 · Double-strand breaks: A high-risk lesion

Both DNA strands are interrupted at or near one genomic location.

Correct joining requires preserving the original chromosomal organization.

Misrepair can yield deletions, inversions, translocations, or other aberrations.

Unrepaired lesions can trigger cell-cycle arrest or cell death.

Slide 31 · DNA damage and potential outcomes

Primary injury

Possible outcome

Pathologic implication

Single-base damage

Enzymatic correction or mutation

Sequence-level alteration

Single-strand break

Repair or persistent injury

Genome maintenance stress

Double-strand break

Faithful or aberrant rejoining

Chromosomal rearrangement

DNA–protein crosslink

Impaired DNA processing

Complex molecular injury

Each entry is qualitative: The lesion does not dictate a single inevitable outcome.

Slide 32 · Homologous recombination: One DSB repair route

Homologous recombination is a recognized mammalian repair pathway.

Repair uses a homologous DNA sequence to guide reconstruction.

Successful repair can restore sequence integrity.

Repair fidelity influences whether irradiated cells retain genomic damage.

Slide 33 · Nonhomologous end joining: A frequent DSB route

Nonhomologous end joining (NHEJ) is described as the more common DSB repair pathway.

The broken DNA ends are reconnected without the same template-based mechanism.

Joining errors can cause small deletions or duplications.

Aberrant rejoining can also produce translocations and inversions.

Slide 34 · Cell fate follows DNA injury and repair

Effective repair may preserve viability and tissue reconstitution.

Persistent injury can inhibit division or induce cell death.

Aberrant repair may permit survival with unstable genetic information.

DNA damage

Repair and recovery

Residual DNA damage

The ultimate outcome depends on the lesion and repair fidelity

Slide 35 · Cell-cycle checkpoints limit propagation

Checkpoints can arrest replication of cells carrying DNA breaks.

Failure to arrest permits chromosomal lesions to persist through cell division.

Surviving damaged clones may accumulate additional transforming events.

The transition to cancer can occur after a prolonged latency.

Slide 36 · Early and late injury are mechanistically distinct

Early injury reflects depletion of proliferative cells and acute tissue dysfunction.

Late injury reflects cumulative vascular damage and stromal fibrosis.

Carcinogenesis depends on surviving genetically altered cells.

Latency varies with the tissue, radiation exposure, and lesion.

Slide 37 · Whole-body versus localized irradiation

Large exposed volumes can threaten multiple regenerative organs at once.

Systemic syndromes differ from the injury caused by a focal therapeutic field.

Whole-body radiation effects escalate as exposure increases.

Localized

Small treatment field

Whole-body

Multiple proliferative organs

Delayed

Persistent vascular / stromal effects

Slide 38 · Total-body radiation: Broad syndrome pattern

Exposure band

Predominant site

Dominant manifestations

0–1 Sv

No dominant site

Little or no acute symptomatology

1–2 Sv

Lymphocytes

Lymphopenia / granulocyte changes

2–10 Sv

Bone marrow

Cytopenias, bleeding, vomiting

10–20 Sv

Small intestine

Diarrhea, fever, fluid/electrolyte loss

>50 Sv

Brain

Ataxia, coma, convulsions

Textbook schematic categories; These bands should not be treated as clinical triage thresholds.

Slide 39 · Acute radiation syndromes: Severity progression

As systemic exposure rises, injury extends beyond isolated circulating lymphocytes.

Marrow suppression impairs host defense and hemostasis.

Greater exposures damage gastrointestinal barrier function.

At extreme exposures, severe central nervous system manifestations occur.

Slide 40 · Lymphoid tissues are highly radiosensitive

Lymphocytes are depleted directly in blood and lymphoid organs.

High-dose, large-field exposure can produce severe lymphopenia within hours.

Lymph nodes and spleen may shrink as lymphocytes are lost.

Regeneration requires survival of competent lymphoid precursors.

Slide 41 · Hematopoietic injury unfolds over time

Different circulating blood cells have different survival times.

A marrow insult first reduces rapidly renewed populations.

The temporal pattern of cytopenias reflects cellular turnover and marrow reserve.

Hours

Lymphopenia

Days

Neutropenia

~1 week

Thrombocytopenia

2–3 weeks

Anemia

Slide 42 · Neutropenia after marrow irradiation

A brief rise in the circulating neutrophil count may precede neutropenia.

Neutropenia becomes apparent within several days.

Counts may reach their nadir during the second week.

Recovery can take months after survivable exposure.

Slide 43 · Thrombocytopenia after marrow irradiation

Thrombocytopenia appears around the end of the first week.

Platelet nadir generally occurs after the granulocyte nadir.

Low platelets contribute to the hemorrhagic consequences of marrow injury.

Recovery depends on surviving hematopoietic precursors.

Slide 44 · Anemia develops later than other cytopenias

Red cells circulate much longer than granulocytes or platelets.

Anemia may become evident after 2–3 weeks.

It can persist for months while erythropoiesis recovers.

Timing is a pathophysiologic clue to marrow rather than isolated blood-cell damage.

Slide 45 · Peripheral blood kinetics after irradiation

Lineage

Typical timing

Explanation

Lymphocytes

Within hours

Direct lymphocyte killing

Granulocytes

Several days; Nadir ~week 2

Rapid turnover

Platelets

From ~week 1; Later nadir

Intermediate survival

Erythrocytes

Anemia after 2–3 weeks

Longer circulating lifespan

Timings are descriptive textbook observations after significant exposure; Individual courses vary.

Slide 46 · Marrow aplasia may be reversible or permanent

Sublethal injury may allow counts to normalize.

Very high exposure can eliminate hematopoietic stem cells.

Permanent aplasia is marked by failure of blood-count recovery.

Stem / progenitor damage

Viable cells remain → recovery

Stem cells destroyed → persistent aplasia

The difference is survival of the regenerative compartment

Schematic

Slide 47 · Organ-specific acute radiation injury

Tissue

Early manifestation

Biologic basis

Skin

Erythema, edema

Epidermal and vascular response

Gastrointestinal tract

Mucosal damage / ulceration

Crypt-cell loss

Bone marrow

Multilineage cytopenias

Progenitor depletion

Gonads

Germ-cell injury

Highly proliferative cell loss

Qualitative organ patterns summarized, Fig. 9.16 and accompanying text.

Slide 48 · Skin: Early and delayed consequences

Early skin manifestations include erythema and edema.

Pigment change can evolve over weeks to months.

Later changes include skin atrophy and increased cancer risk.

Chronic radiation dermatitis also shows dermal fibrosis and vascular ectasia.

Slide 49 · Gastrointestinal tract: Barrier injury

Renewing gastrointestinal mucosa is susceptible to proliferative-cell damage.

Early effects include mucosal injury and ulceration.

Severe whole-body exposure can produce diarrhea and fluid-electrolyte imbalance.

The wall may become fibrotic late after irradiation.

Slide 50 · Gonads: Germ-cell injury

Spermatogenic cells and ovarian germ cells are radiosensitive.

Gonadal exposure can cause temporary or permanent impairment of fertility.

Late tissue atrophy and fibrosis can follow more severe injury.

Magnitude and reversibility depend on exposure and viable cell reserve.

Slide 51 · Lung: Acute and chronic effects

Radiation-exposed lung may develop edema and acute respiratory injury.

Interstitial fibrosis may appear over subsequent months or years.

Late fibrosis impairs tissue architecture in previously irradiated fields.

Pulmonary toxicity must be understood in relation to exposed lung volume.

Slide 52 · Brain: Maturity influences cellular response

Adult neural parenchymal cells are comparatively resistant to division-dependent killing.

The developing embryonic nervous system is markedly more vulnerable.

At extreme whole-body exposures, severe neurologic syndromes occur.

Relative cellular resistance does not imply complete clinical protection.

Slide 53 · Radiation: Chromosomal morphology

Deletions, translocations, and chromosomal fragmentation may follow injury.

Mitotic spindle abnormalities can accompany aneuploidy or polyploidy.

Changes are consequences of genome injury, not specific proof of cancer.

DNA double-strand breaks

Rearrangements / fragments

Abnormal mitosis

Schematic

Slide 54 · Nuclear changes in surviving irradiated cells

Nuclear swelling, chromatin clumping, and condensation may occur.

Pleomorphic or multinucleated giant cells can persist long after exposure.

Severe injury may produce pyknosis, nuclear lysis, or apoptosis.

Irradiated surviving cells can show atypical nuclei

Swollen / irregular

Pleomorphic

Multinucleated

Schematic • not diagnostic microscopy

Slide 55 · Cytoplasmic morphology of radiation injury

Cell swelling can accompany nuclear injury.

Mitochondria and endoplasmic reticulum may show degenerative change.

Focal plasma-membrane defects can develop.

Multiple organelle alterations indicate injury is not restricted to DNA.

Slide 56 · A diagnostic pitfall: Radiation atypia

Pleomorphic nuclei and abnormal mitoses may resemble residual malignancy.

Radiation history and treatment field are essential interpretive context.

Atypia alone must not be equated with viable recurrent tumor.

Anatomic architecture and additional histologic evidence remain important.

Radiation effect

Viable malignant tumor

Pleomorphic nuclei and giant cells can mimic malignancy

Integrate history + morphology + viable tumor architecture

Slide 57 · Acute vascular changes after irradiation

Early vessel changes may consist primarily of dilation.

Greater injury causes endothelial swelling and vacuolation.

Severe endothelial damage can lead to wall necrosis or rupture.

Thrombosis may occur when vascular integrity is disrupted.

Slide 58 · Late vascular remodeling narrows the lumen

Endothelial proliferation and intimal collagen deposition develop later.

Hyalinization and thickened intima narrow affected vessels.

Advanced lesions may obliterate the vascular lumen.

Chronic flow reduction promotes ischemic parenchymal atrophy.

Progressive luminal compromise

Early dilation

Intimal thickening

Marked stenosis

Schematic vascular cross-sections

Slide 59 · Why radiation produces fibrosis

Parenchymal-cell loss creates a need for tissue replacement.

Vascular injury amplifies ischemic cell loss.

Inflammatory signals and fibroblast activation favor collagen accumulation.

The final result may be scarring, adhesions, and tissue contraction.

Cell injury / loss

Vascular ischemia

Inflammation and fibroblast activation

Collagen deposition → scar / contracture

Slide 60 · Radiation fibrosis: The time course

Fibrosis can emerge weeks to months after treatment.

Later vascular narrowing can continue to impair perfusion.

Replacement collagen alters elasticity and organ function.

The scar lies within the irradiated field rather than representing new viable parenchyma.

Slide 61 · Common anatomic settings for fibrosis

Lung fibrosis can follow irradiation involving pulmonary parenchyma.

Salivary gland fibrosis can follow head-and-neck radiotherapy.

Colorectal and pelvic tissues may scar after treatment of pelvic malignancies.

Local tissue anatomy governs the eventual functional impairment.

Slide 62 · Salivary gland: A field-specific example

Irradiated gland tissue may lose functional parenchyma.

Interstitial collagen progressively replaces damaged tissue.

Arterioles may show fibrointimal thickening and sclerosis.

The combined parenchymal and vascular damage explains persistent dysfunction.

Slide 63 · Vascular injury and impaired tissue repair

Late radiation lesions may evolve after early cell death subsides.

Chronic ischemia limits normal regeneration.

Repair can proceed by scar rather than restoration of specialized tissue.

Endothelial damage

Reduced tissue perfusion

Ongoing ischemic injury

Repair by fibrosis

Schematic

Slide 64 · Cancer arises from surviving altered cells

DNA damage alone does not guarantee malignant transformation.

Incorrect repair can produce persistent chromosomal changes.

Additional transforming events may accumulate over time.

Cancer may develop after prolonged latency in a surviving proliferative clone.

Slide 65 · Carcinogenesis following radiation exposure

Mutations arise when DNA injury is misrepaired or persists.

Checkpoint escape allows genetically abnormal cells to replicate.

Radiation-related neoplasia is a delayed outcome rather than an acute syndrome.

Ionizing radiation

DNA double-strand break

Aberrant repair / genomic instability

Additional events → neoplasia

Schematic

Slide 66 · Epidemiologic evidence of radiation-associated cancer

Atomic-bomb survivor cohorts demonstrate excess leukemias and several solid tumors.

Chernobyl-associated exposure is linked to thyroid cancer in affected populations.

Fallout exposures and cancer survivors treated with radiation provide further evidence.

Risk varies with age, tissue, radiation type, and exposure history.

Slide 67 · Low-dose cancer risk is harder to quantify

Small increments in long-term risk require very large cohorts to detect.

Dosimetry uncertainties and background cancer incidence complicate inference.

Stronger evidence at higher doses from greater uncertainty at lower doses.

A numerical risk estimate should not be inferred from the slide examples alone.

Slide 68 · Children: Additional vulnerability to late cancer

Children have more dividing cells and longer remaining lifespans.

Small but measurable risks after repeated pediatric CT exposures.

Chest irradiation during adolescence has been associated with later breast cancer.

Clinical imaging still requires balancing justified diagnostic benefit against radiation risk.

Slide 69 · Second malignancies after radiotherapy

Radiotherapy survivors may develop malignancies after long latency.

Leukemia, myelodysplastic syndrome, and solid second tumors.

The risk is a late stochastic effect distinct from deterministic tissue fibrosis.

Interpret a post-treatment lesion in light of prior irradiation and tumor history.

Slide 70 · Radon: An internally deposited alpha source

Radon is generated in the decay chain of uranium.

Polonium decay products emit alpha particles and can lodge in the lung.

Chronic inhalation provides a biologically plausible route to lung carcinogenesis.

Uranium decay

Radon gas

Polonium daughters

Alpha irradiation of lung

Chronic inhalational exposure → carcinogenic risk

Slide 71 · Radon and concurrent tobacco exposure

Elevated radon concentrations may occur in occupational or domestic settings.

Occupational lung cancer risk among exposed miners.

Household radon is also a health concern, particularly with concurrent smoking.

The hazard reflects alpha-emitting decay products deposited in respiratory tissue.

Slide 72 · Case: Pleomorphic cells after radiotherapy

Clinicopathologic problem

A biopsy from a previously irradiated site contains scattered multinucleated giant cells with bizarre nuclei and dense stromal fibrosis. The requisition asks whether the original cancer has persisted.

Which findings can be caused by irradiation, and what is the diagnostic pitfall?

Slide 73 · Case analysis: Separate atypia from viability

Radiation damage can cause giant cells, nuclear pleomorphism, and abnormal mitoses.

Fibrosis and chronic vascular alterations support a treatment-affected field.

These features may mimic malignancy; They do not by themselves establish viable tumor.

Clinical history and evidence of true residual neoplastic architecture guide interpretation.

Slide 74 · Case: Sequential cytopenias after exposure

Clinicopathologic problem

Following substantial whole-body irradiation, a patient develops early lymphopenia, then neutropenia, thrombocytopenia, and later anemia.

Why do the cell counts decline in this sequence?

Slide 75 · Case analysis: Turnover drives blood-count timing

Direct lymphocyte loss can be evident within hours.

Granulocytes are replaced rapidly, so neutropenia appears within days.

Platelet counts fall later; The longer-lived erythrocyte pool delays anemia.

Recovery requires surviving hematopoietic precursors.

Slide 76 · Case: Delayed organ injury

Clinicopathologic problem

Months after radiotherapy, an organ within the treated field becomes indurated and less functional. Histology shows subintimal vessel thickening and increased interstitial collagen.

Explain the causal link between vascular change and fibrosis.

Slide 77 · Case analysis: Ischemia feeds the fibrotic response

Endothelial injury initiates intimal thickening and luminal narrowing.

Impaired perfusion produces chronic parenchymal ischemia.

Loss of regenerative cells and fibroblast activation increase collagen deposition.

Organ dysfunction reflects both parenchymal depletion and structural scarring.

Slide 78 · Synthesis: Four integrated pathways

Energy transfer and ionization initiate molecular damage.

DNA injury preferentially disrupts regenerating tissues and cell division.

Endothelial injury generates delayed ischemia and fibrosis.

Misrepaired DNA in surviving cells creates long-term neoplastic potential.

Slide 79 · Final integration: Effect, substrate, latency

Effect

Primary substrate

Typical temporal logic

Acute cytopenia

Marrow / lymphoid cells

Early loss of short-lived lineages

Delayed fibrosis

Vessels, stroma, parenchyma

Months–years after injury

Radiation atypia

Irradiated surviving cells

May persist long after exposure

Secondary cancer

Surviving mutant clone

Delayed, often years later

Mechanisms and timing are drawn from the radiation-injury discussion.

Slide 80 · Primary reference and scope

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11th edition (2026).

The radiation-injury discussion covers ionization, dose concepts, tissue sensitivity, morphology, fibrosis, and cancer risk.

Conceptual schematics in this lecture are original editable drawings, not reproductions of textbook figures.