Clinical Response of Normal Tissues

Parag Roy LOK NAYAK HOSPITAL

2 Cells and Tissues

• Majority of radiation effect on normal tissues attributed to cell killing,

• But some cannot• Nausea or vomiting hours after irradiation of abdomen• Fatigue of patients with large volume irradiation• Acute edema or erythema from radiation-induced acute

inflammation and vascular leakage• Somnolence after cranial irradiation

3 Cells of normal tissues

• Not independent structure • Complete integrated structure• Cell death and birth balanced to maintain tissue organization• Response to damage governed by

• Inherent cellular radiosensitivity• Kinetics of the tissue• The way cells are organized in the tissue

4 Weaknesses in Single-Cell Study

Individual cells Continuous monotonic relationship between dose and fraction of

cells killed (e.g., loss of reproductive integrity) Tissues

No effect observed after small doses Effects observable increase after threshold reached

Conclusion Killing a few cells in a tissue matters very little, requires more

massive killing Also, time between irradiation and expression of damage varies

greatly among tissue types.

5 Cells and tissues, continued

➡ Cell death after irradiation mainly occurs as cells attempt to divide➡ Tissues with rapid cell turnover consequently show damage more

quickly (e.g., hours for intestinal epithelium, days for skin mucosa)➡ Tissues where cells rarely divide may have long latency to express

damage➡ Radiation damage to cells and tissues already on the path to

differentiation is of little consequence➡ Interestingly

➡ Cells that are differentiating may appear more radioresistant than stem cells

➡ In fact, the fraction of cells surviving a given dose may be identical (at the single-cell level)

6 Early (Acute) and Late Effects

Radiation effects commonly divided into early and late Shows different patterns of response to dose fractionation Dose-response relationships characterized by a/ß ratios

Late effects more sensitive to changes in fractionation than early effects

Early (acute) effects result from death of large number of cells and occur within weeks to days of irradiation in tissues with rapid rate of turnover

7 Examples of early effected tissues

Examples Epidermal layer of skin Gastrointestinal epithelium Hematopoietic system

Response is determined by hierarchical cell lineage composed of stem cells and differentiating offspring.

Time of onset correlates with lifespan of mature functional cells

8 Example of late-effected tissues

Late effects appear after delay of months or years Occur predominantly in slowly proliferating tissues

Lung Kidney Heart Central nervous system

9 Distinction between early and late effects Progression distinguishes early and late effects Acute (early) damage

Repaired rapidly because of rapid proliferation of stem cells May be completely reversible

Late damage May improve But never completely repaired

10 Mechanism of late effect

Reactive oxygen species from NADPH Oxidases Mitochondria Superoxide anion

Role of Inflammation Radiation-Induced Vascular Changes Possible Metabolic Changes by carbonic anhydrase 9

11 Functional Subunits (FSUs) in Normal Tissues Fraction of cells surviving determines the success (or failure) of

radiation therapy If a single cells survives it may result in regrowth of the tumor

Normal tissue tolerance for radiation depends on Ability of clonogenic cells to maintain sufficient number of mature

cells suitably structured to maintain organ function Survival of clonogenic cells and organ function (or failure) depends

on the structural organization of the tissue Many tissues are thought to consist of functional subunits (FSUs)

12 Functional Subunits (FSUs)

Some tissues FSUs Are discrete, anatomically delineated structures whose relationship

to the tissue function is clear Example kidney nephron, lobule in liver, acinus in the lung

In other tissues, no clear anatomic demarcation. Examples skin, mucosa, spinal cord

Radiation response of two tissue types quite different

13 The Human Kidney Nephron

14 Structure of Skin

The skin consists of two layers: the epidermis and the dermis. Beneath the dermis lies the hypodermis or subcutaneous fatty tissue.

15 Survival of Structurally defined FSUs toRadiation Exposure Depends on survival of one or more clonogenic cells within the FSU Surviving clonogens cannot migrate from one FSU to another Each FSU is small and autonomous, low doses can deplete the

clonogens in it. Example kidney composed of large number of small FSUs (e.g., nephrons)

each independent of the neighbor Survival of a nephron following irradiation depends on survival of at least

one clonogen within it therefore on the initial number of renal tubule cells per nephron and their radiosensitivity

Because it is small, it can be easily depleted of clonogens by low doses, Therefore the kidney has a low dose tolerance

16 Other structurally defined FSUs

Other organs that resemble the kidney include Those with branching treelike structure of ducts and vasculature that

terminates in end structure or lobules of parenchymal cells Lung Liver Exocrine organs

Many of these have low tolerance to radiation

17 Radiation response structurally undefined FSUs Clonogenic cells in these systems not confined to one particular

FSU Cells can migrate from one FSU to another Allows repopulation of a depleted FSU Example re-epithelialization of a denuded area of skin can occur

either from surviving clonogens within denuded area or by migration from adjacent areas

18 Tissue Rescue Unit

Concept proposed to link survival of clonogenic cells and functional survival

Defined as minimum number of FSUs required to maintain tissue function

Assumes Number of TSUs is proportional to number of clonogenic cells FSUs contain constant number of clonogens FSUs can be repopulated from single clonogen

19 Issues with FSUs

Some tissues defy classification Crypts of jejunum (structurally

well defined but surviving crypts can/do migrate from one crypt to another to repopulate depleted neighbors

20 Volume Effect in Radiotherapy

Total dose that can be tolerated depends on volume irradiated Tolerance dose (TD) is defined as the dose that produces an

acceptable probability of a treatment complication. Includes objective criteria like radiobiology and subjective factors like

socioeconimic, medicolegal etc Serial and parallel structure

21 Dose vs Complications

Spatial arrangement of FSUs in tissue is critical Serially arranged FSUs

Example spinal cord integrity of each FSU is critical to organ function Elimination of any FSU in this system can result in measurable

probability of complication Radiation damage shows binary response threshold below which is

normal function, above which there is loss of function

22 Dose vs. Complications

23 Clinical tolerance

For both kidney and lung, clinical tolerance depends on volume irradiated

Both organs are sensitive to irradiation of their entire volume, but small volumes can be treated to much higher doses Considerable functional reserve capacity (only 30% of organ required to

maintain function under normal physiologic conditions) Inactivation of small number of FSUs does not lead to loss of organ

function Implication there is a threshold volume of irradiation below which

functional damage does not develop, even after high dose irradiation Above threshold, damage is exhibited as a graded response (increasing

severity of functional impairment) rather than binary-all or nothing response

24 Clinical tolerance- structurally undefined FSUs Example - Skin and mucosa have no well defined FSUs Respond similarly to defined FSUs with parallel architecture Do not show volume effect at lower doses where healing can

occur from surviving clonogens The severity of skin reaction is relatively independent of the area

irradiated because healing occurs through regeneration from clonogens scattered throughout the tissue

Therefore there is a volume effect (in practice)

25 Radiation Pathology of Tissues

Response of tissue to radiation depends on 3 factors Inherent sensitivity of the individual cells Kinetics of the tissue as a whole Way the cells are organized in the tissue

These factors combine to account for the substantial variation in radiation response characteristics of different tissues

26 Casaretts Classification

Suggested classification of mammalian cell radiosensitivity based on histologic observation of cell death

Divide parenchymal (functioning) cells into 4 major categories, I-IV Supporting structures (e.g., connective tissue and endothelial cells

of small blood vessels) were regarded as intermediate in sensitivity between groups II and III of parenchymal cells

Most sensitive cells die mitotic death after irradiation Most cells that don't divide require very large doses to kill them Lymphocyte

Does not usually divide Dies an interphase death One of the most radiation sensitive cells

27 Casaretts Classification of Mammalian CellRadiosensitivity

28 Classification

Vegetative Intermitotic Cells.(VIM) Undifferentiated rapidly dividing cells which generally have a quite

short life cycle. Examples are erythroblasts, intestinal crypt cells and basal cells of the skin.

Essentially continuously repopulated throughout life Differentiating Intermitotic Cells (DIM)

Actively mitotic cells with some level of differentiation. Spermatogonia are a prime example as well as midlevel cells in differentiating cell lines.

Have substantial reproductive capability but will eventually stop dividing or mature into a differentiate cell line

29 Classification..cont

Reverting Postmitotic Cells (RPM) Does not normally undergo division but can do so if called upon by the

body to replace a lost cell population. These are generally long lived cells. Mature liver cells, pulmonary cells and kidney cells make are examples

of this type of cell. Fixed Postmitotic Cells (FPM)

Most resistant to radiation Highly differentiated and lost ability to devide May have long (neurone) and short life span (granulocyte)

30 Michalowski Classification

Tissues follow either a hierarchical (H) or flexible (F) model Within tissues 3 distinct categories of cells

Stem cells continuously divide and reproduce to give rise to both new stem cells and cells that eventually give rise to mature functional cells.

Functional cells, which are fully differentiated; they are usually incapable of further division and die after a finite life span, though the life span varies enormously among different cell types. Example- circulatory granulocytes

Between these two extremes are maturing partially differentiated cells ; these are descendants of the stem cells, still multiplying as they complete the process of differentiation. In the bone marrow, for example, the erythroblasts and granuloblasts represent intermediate compartments

31 H-type & F-type populations

Hierarchical (H-type) populations- The cell types that progress from the stem cell through the mature cell with nonreversible steps along the way.

They include bone marrow, intestinal epithelium, epidermis and many others.

Flexible tissue(F-type) populations- The cell lines in which the adult cells can under certain circumstance be induced to undergo division and reproduce another adult cell.

Examples include liver parenchymal cells, thyroid cells and pneumocytes as well as others.

32 Growth Factors

Radiation causes injury of normal tissue through cell killing, But in addition to mitotic and apoptotic cell death, radiation can

induce changes in cellular function secondary to tissue injury Altered cell-to-cell communication Inflammatory responses Compensatory tissue hypertrophy of remaining normal tissue, and Tissue repair processes

Recognition of these "non-cytocidal" radiation effects has enhanced understanding of normal tissue radiation toxicity

IL-1,6- rdioprotector of hematopoetic cells, Fibroblastic growth factor inhibits radiation induced apoptosis, TGF- induce pneumonitis

33 General Organ System Responses

Individual Organ/Tissue sensitivity to radiation injury Discussion-

Skin Hematopoietic system Digestive system Lung Kidneys Bladder Nervous system Genitalia

34 Hemopoietic (blood and lymph)

Refers to the parenchymal cells of the bone marrow and the circulating blood.

Does not refer to the vessels themselves Critical cells are the marrow blast cells and circulating small

lymphocytes. Non-circulating lymphocytes and other circulating white cells fairly

radioresistant Red Blood Cells are the radioresistant cell Irradiation of a small region of the body generally has no effect on

circulating levels An exception is lymphocyte counts following therapy level doses

to the chest.

35 Hemopoietic (blood and lymph)

Irradiation of a majority of the bone marrow will cause marked decreases in circulating cell levels post irradiation. Platelets at 2-4 days White cells at 5-10 days Red cells at 3-4 weeks

Due to irradiation of stem cells of these cell lines.

36 Hemopoietic (blood and lymph)

Radiation doses to the entire marrow of greater than 8 gray are quite likely to result in marrow death and patient death unless a successful marrow transplant can be performed.

Used in pre transplant marrow sterilization B lymphocytes has life span of 7 weeks and Plasmacyte has 2-3

days T lymphocyte has 5 months of life span Total body irradiation leads to a rapid fall in the number of

circulating B and T lymphocytes Total lymphoid irradiation to a dose of 30 to 40 Gy is used for the

treatment of lymphomas and leads to a long-lasting T-cell lymphopenia (used in organ transplant).

37 Skin

Composed of epidermis, dermis, hypodermis

Takes about 14 days from the time a newly formed cell leaves the basal layer to the time it is desquamated from the surface

38 Skin

A few hours after doses > 5 Gy, there is early erythema similar to sunburn, is caused by vasodilation, edema loss of plasma constituents from capillaries.

Erythema develops in 2nd to 3rd week of a fractionated, followed by dry or moist desquamation resulting from depletion of the basal cell population

higher doses, at which there are no surviving stem cells, moist desquamation is complete, healing must occur by migration of cells from outside the treated area.

Skin & oral mucosa, the total dose tolerated depends more on overall time than on fraction size.

Telangiectasia developing more than a year after irradiation reflects late developing vascular injury.

39 Skin

Little or no reaction below 6-8 gray

Erythema w/a early and late effects at 10 gray and above.

Early effects Erythema Dry desquamation Moist desquamation Necrosis

Late effects occur and increase with dose

Recovers well from fairly high doses but late effects seen Thinning of skin Pigmentation or

depigmentation Loss or thinning of hair. Loss or thinning of

subcuntaneous fat Cancer induction years

later.

40

Sources of radiation injury Solar UV

Probably major threat for most people Diagnostic x-ray

Fluoroscopy Especially cardiac CT High speed spiral in juveniles

Radiation therapy Modern techniques keep dose low below 5 gray Exception is when skin is primary target.

41 Digestive System

Extends from mouth through rectum Sensitivity of individual parts rests with the number and

reproductive activity of the stem cells in the basal mucosal layer Mouth and esophagus relatively resistant Stomach more sensitive and has more secretory cells Small bowel very sensitive Colon and Rectum similar to esophagus

42 Order of events in HNCWeek Consequences

1st week Asymptomatic to slight focal hyperemia due to dilatation of capillaries, Increased sensitivity with alcohol or tobacco, chemotherapy, infection (oral candidiasis, herpes simplex virus),or immunosuppression (HIV).

2nd week Increasing pain and loss of desire to eat. Sense of taste is altered; bitter and acid flavors are most changed, with less change with salty and sweet tastes. Basal cells are denuded and patchy mucositis

3rd week Mucositis and swelling with depletion of gland secretions leading to difficulty in swallowing. Mucositis plaques are confluent.

4th week Confluent mucositis sloughs, resulting in denuded lamina propria. Mucosa becomes covered by fibrin and polymorphonuclear leukocytes.

5th week Maximum radiation damage apparent by this time. Extreme sensitivity to touch, temperature, and grainy food. Xerostomia and poor oral hygine

43 Early effects are mucosal depopulation

Clinical soreness and possible ulceration With very high doses bleeding and necrosis Loss of secretory cells

Stomach and Intestine decreased mucus Decreased digestive enzyme production Decreased hormone production

Late effects Repopulation functional recovery partial Epithelial metaplasia loss of function Scarring severe loss of function

Chronic clinical signs Stricture - obstruction of GI tract

Surgical mediation required.

44 Digestive Track

Esophagus- Esophagitis and increased thickness of squamous layer

Substernal burning with pain on swallowing at about 10 to 12 days after the start of therapy

Stomach- nausea and vomiting, delayed gastric emptying and epithelial denudement are the two main early radiation effects.

Dyspepsia may be evident in 6 months to 4 years and gastritis in 1 to 12 months

Intestine- Acute mucositis frequently occurs, with symptoms such as diarrhea or gastritis,

45 Lungs

One of the most radiosensitive of late responding organs Intermediate to late responding tissue

Reverting Post mitotic populations of epithelium 10 gray single dose or 30 gray fractionated to the whole lung cause

progressive fibrosis Type II pneumocyte is critical cell for edema

Edema is acute toxicity (radiation pneumonitis- 2-6 months) Fibrosis is the late effect- several months to years

The lung has large functional reserve Dose to less than ½ lung has minimal clinical effect Increased toxicity with bleomycin, cyclophosphamide

46 Lung structure

47 Kidneys

Radiosensitive late-responding critical organ Radiation to both kidneys to a modest dose of about 30 Gy in 2-Gy

fractions results in nephropathy with arterial hypertension and anemia.

FSUs are arranged in parallel, with each containing only about 1,000 stem cells

Five distinct clinical syndromes occur acute radiation nephropathy, chronic radiation nephropathy, benign hypertension, malignant hypertension, and hyperreninemic hypertension secondary to a scarred encapsulated

kidney

48 Simplified pic

49 Liver

Large organs which are fairly radiation sensitive Major radiation threat is from radiation therapy fields which include

these organs Vascular injury may play an important role. Whole organ doses of 30 gray are lethal FSU are arranged in parallel Greater tolerance if partially irradiated Fatal hepatitis if 35 Gy in whole liver is given Life span of hepatocyte is about 1 year

50 The structure of the livers

functional units, or lobules. Blood enters the lobules

through branches of the portal vein and hepatic artery, then flows through small channels called sinusoids that are lined with primary liver cells (i.e., hepatocytes).

The hepatocytes remove toxic substances, including alcohol, from the blood, which then exits the lobule through the central vein (i.e., the hepatic venule).

51 Male Reproductive System

Adult sperm are Fixed Post Mitotic cells But, chromosomal damage may be passed on to a fetus. Mutations can

result. Germinal cells very sensitive though

0.1 gray temporary reduction of no of spermatozoa 0.15 gray to testis causes temporary sterility 2 gray leads aazospermia lasting several year 6-8 gray to testis causes permanent sterility in 2gy/fr

Diagnostic x-ray and nuclear medicine studies not a threat to function Radiation therapy near testis probably cause temporary sterility Radiation therapy including testis causes sterility and possibly loss of

function. Functional sperm present 1-2 weeks after 1st dose

52 Female Reproductive System

Radiation therapy is major sterility threat 6.25 Gray to both ovaries expect sterility Oocytes do not divide thus no repopulation

Radiation therapy is hormonal function threat. Hormonal function decreased/lost above 25 gray May require hormonal supplementation

Oocytes do not divide and Themselves relatively resistant Chromosomal damage carried on and may become evident after

fertilization. Ovarian sensitivity more tied to follicular cells which support oocytes during

During follicle development there is great cellular growth activity in these cells.

Inactive follicular cells are less sensitive

53 Eyes

Eyes are a major dose limiting structure The lens is vary sensitive to radiation

Cataract formation is major effect Seen with doses as low as 2 gray Very likely 6.5 to 11.5 Gy

Occupational dose from diagnostic x-ray is a threat for cataract formation. Wear eye shields, esp. during fluoroscopy

Major side effect of RT to head and neck

54 Cardiovascular System

Vessels Endothelium is target cell type Endothelial injury causes thrombosis , hemorrhage and necrosis Endothelium can repopulate to limited degree normally Veins are more resistant to RT In vessels after radiation muscle layer are replaced by collagen,

and elasticy is lost, blood flow decreased Arterial damage at 70Gy and capillary are at 40Gy

55 Heart

Considered resistant Late effects maybe seen years later. Acute or Fibrosing pericarditis most common At higher doses myocardial fibrosis seen

Late effects seen are slowly progressive Revealed or exacerbated by chemotherapy

Diagnostic radiation not usually a threat >50% of heart vol is irrediated then pericarditis occur at 20Gy Chemotherapy like doxorubicin, dacarbazine, dactinomycin

increases risk

56 Bone and Cartilage

Mature bone is composed of FPM cells from hierarchical cell lines – At high RT doses osteonecrosis and fractures seen

D/t loss of mature osteocytes Growing cartilage cells at growth plate are a target at risk. Especially at < 2

yrs old. Causes stunted growth and possibly deformity due to death of

chondroblasts High dose to joint can cause ‘dry’ joint Diagnostic exposure in children from Multi-slice spiral CT can be enough to

at least cause some growth arrest. Radiation Therapy exposure will cause permanent growth arrest in open

growth plate of a young person

57 Central Nervous System

CNS is considered quite radioresistant in adults. Development continues to 12 years of age therefore whole brain dose

can reduce development Glial cells and endothelial cells are the critical cells of interest as slow

rate of turnover. RT usually avoided in children. Increasing volume or dose the effects

Large volumes irradiated above 40 Gray lead to decreased function. Spinal cord is serial structure Early injury- Lhermittes sign (reversable) Late injury- demyelination and necrosis of white matter and vasculopathy

58 Spinal Cord Structure

Two major tissues Gray matter - nerve cell bodies

and thousands of connections between nerves.

White matter (composed of nerve axon fibers) travels from the spine to the brain.

Ventral root carries motor axon fibers from cells in gray matter out to muscles.

Incoming sensory signals pass through dorsal root into the grey matter

59 LENT AND SOMA

European Organization for Research and Treatment of Cancer (EORTC) and the Radiation Therapy Oncology Group (RTOG), formed working groups to update their system for assessing late injury to normal tissues

This led to the Late Effects of Normal Tissue (LENT) conference in 1992

This conference led to the introduction of the SOMA classification for late toxicity

SOMA is an acronym for subjective, objective, management criteria with analytic laboratory and imaging procedures

60 The SOMA Scoring System

Subjective- injury, if any, will be recorded from the subject’s point of view that is, as perceived by the patient

Objective—in which the morbidity is assessed as objectively as possible by the clinician during a clinical examination

Management—which indicates the active steps that may be taken in an attempt to ameliorate the symptoms

Analytic—involving tools by which tissue function can be assessed even more objectively or with more biologic insight than by simple clinical examination

There is no grade 0, because that would indicate no effect, and no grade 5, because that would indicate totality, or loss of an organ or function.

61 Anatomic Sites for Which There Are LENT and SOMA Scales

62 Central Nervous System SOMA

63 LENT and SOMA Scoring System and Grading Categories

Grade I Grade II Grade III Grade IVSubjective (pain)

Occasional and minimal

Intermittentand tolerable

Persistent and intense

Refractory and excruciating

Objective (neurological defect)

Barely Detectable

Easily Detectable

Focal Motor sign, vision and disturbances

Hemiplegia, Hemisensory defect

Management (pain)

Occasional nonnarcotic

Regular nonnarcotic

Regular narcotic

Surgical intervenrion

Analytic (CT, MRI, Lab Tests)

64 QUANTEC

Quantitative Analysis of Normal Tissue Effects in the Clinic Published in the International Journal of Radiation Oncology,

Biology, and Physics in 2010 (IJROBP)

65 Character/Content of Emami and QUANTEC

66 Implications of QUANTEC

Different mechanisms for radiation-induced injury in different organs

Serially arranger organ have steep dose–response curves at doses beyond an apparent critical threshold

Several neural structures exhibit a similar threshold dose for injury, so there is common mechanism of injury

Organs that are classically considered structured in parallel (e.g., lung, liver, parotid, and kidney, analogous to electrical circuits) experience injury at far lower doses and have more gradual dose–response curves compared to series organs

QUANTAC is better quantify the relationship between dose– volume parameters and clinical outcomes.

67

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