L4Chronic radiation exposure

Chronic radiation exposure:

Exposure to ionizing radiation over an extended period of time is called chronic exposure. The

natural background radiation is chronic exposure, but a normal level is difficult to determine due

to variations.

Reaction on radiation exposure according to the radiosensitivity of the tissues:

1. Highly radiosensitive:

1.1. hematopoietic tissues – bone marrow: one-time irradiation of the whole body in the dose of

4 Gy may cause lethal myelodepression in 50% of patients. In case of whole-body irradiation in

the dose of 10 Gy – allogenic bone marrow transplantation is used obligatory in protocol for

treatment of acute leikemias

1.2. gonads: irradiation of testicles in the dose of 1Gy leads to oligospermia, & irradiation of

ovaries in the dose of 10-12 Gy causes amenorrhea

2. Medium radiosensitive tissues:

2.1. GIT: side effects in case of intraabdominal tumors irradiation are:

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nausea,

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vomiting,

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Diarrhea.

Long-term effects are:

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malabsorption syndrome,

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rectal ulcers,

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bleeding

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strictures

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fistulas

2.2. Skin:

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erythema

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dry or moist epidermitis

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alopecia

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loss of apocrine glands

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pigmentation/ de pigmentation

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fibrosis

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subdermal layer atrophy

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teleangiectasia

2.3. Nervous system: brain & spinal cord may stand the doses about 50Gy. Complications of the

RT:

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radiation myelitis

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Brown-Sequar s-m (homolateral paralysis & loss of the deep sensitivity)

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Sphincters disorder

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Lermitt’s s-m- parestesias in the hands & legs due to radiation arachnoiditis, but it is

reversable

That’ s why spinal cord may be irradiated on the length less than 10 cm in dose of 40-45 Gy.

Hypertension increases radiosensitivity of the spinal cord.

2.4. Eye:

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2 Gy- causes cataract development

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30-40 Gy – dry eye s-m, loss of defense reflex

2.5. Lungs:

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Acute radiation pneumonitis (duration 1-3 months). Symptoms:

1. cyanosis

2. dyspnea

3. cough

4. hyperpyrexia

5. night sweats

Treatment: steroids – effective only in acute stage

Acute radiation pneumonitis →3-6 month→ fibrosis.

Limit dose for developing of radiation pneumonitis: 7-8 Gy per 1 fraction or 20 Gy per 10

fractions

Delayed effects may be intermediate or late.

Intermediate effects: Prolonged or repeated exposure to low-dose rates from internally

deposited or external sources of radiation may produce:

amenorrhea,

decreased fertility in both sexes,

decreased libido only in the female,

anemia, leukopenia, thrombocytopenia, and

cataracts.

More severe or highly localized exposure causes:

loss of hair,

skin atrophy and ulceration,

keratosis, and telangiectasia,

and ultimately may cause squamous cell carcinomas.

Osteosarcomas may appear years after ingestion of radioactive bone-seeking nuclides such as

radium salts.

Serious injury to exposed organs occasionally occurs after extensive radiotherapy for cancer:

Renal functional changes include a decrease in GFR and tubular function. Acute onset of

clinical manifestations may occur after extremely high doses (after a latent period of 6 mo

to 1 yr) and may include proteinuria, renal insufficiency of varying degree, anemia, and

hypertension. When cumulative kidney exposure is >20 Gy in <5 wk, radiation fibrosis and

oliguric renal failure will occur in about 37% of cases. The remainder will develop variable

changes over a prolonged time.

Large accumulated doses to muscles may result in painful myopathy with atrophy and

calcification. Very rarely, these changes are followed by a neoplastic change, usually a

sarcoma.

Radiation pneumonitis and subsequent pulmonary fibrosis may be severe when lung

metastases are irradiated, and can be fatal after a cumulative dose of >30 Gy if treatment is

not spread over a sufficient period.

Radiation pericarditis and myocarditis have been produced by extensive mediastinal

radiotherapy.

Catastrophic myelopathy may develop after a segment of the spinal cord has received

cumulative doses >50 Gy.

Following vigorous therapy of abdominal lymph nodes (for seminoma, lymphoma, or ovarian

carcinoma), chronic ulceration, fibrosis, and perforation of the bowel may develop.

Skin erythema and ulceration were observed fairly often during the era of orthovoltage x-ray

therapy, but the high-energy photons from modern cobalt-60 units and linear accelerators

penetrate deeply into tissues and have virtually eliminated these complications.

Late somatic and genetic effects: Radiation alters the "information system" of proliferating

somatic and germ cells. With somatic cells this may result in somatic disease--eg, cancer

(leukemia, thyroid, skin, bone) or cataracts--or, as suggested by animal models, in nonspecific

shortening of life. Leukemia from substantial radiation in humans has been observed. It is

postulated that there is no "threshold" dose for leukemia, and that the incidence increases with

dose. Thyroid carcinoma has been observed 20 to 30 yr after x-ray therapy for adenoid and

tonsillar hypertrophy, and x-ray treatment for nonmalignant conditions is now considered

inappropriate except in highly unusual situations. However, several large studies have failed to

show increased thyroid cancer in persons receiving up to 80 mGy to the thyroid delivered by

radioisotopes.

With germ cell exposure, mutations are increased. When mutations are perpetuated by

procreation, animal studies indicate that an increasing number of genetic defectives will be

expressed in the course of generations. Although this has not been demonstrated in man, the

possibility presents serious medical, ethical, and philosophic problems with respect to unborn

generations. It imposes a moral obligation to limit radiation exposure to that which is absolutely

necessary for valid diagnostic or therapeutic purposes and to strictly control occupational

exposure. The potential harm, however, should be kept in perspective. Some investigators

believe that no measurable effects will occur below a certain threshold, while others insist that

any radiation is potentially harmful.

CRES: chronic radiation exposure syndrome.

Persons affected by the IR are divided on 3 groups:

affected by external irradiation

those, who have contact with powder-life, gas or liquid alpha- & beta-radioactive

substances (they have a danger of ingestion, inhalation, trapping into the organism)

people affected by mixed external & internal irradiation

Most of the radioactive substances have the ability of accumulation & deposition in certain

organs & tissues (organotropic).

Routs of radioactive substances trapping into the organism:

1. respiratory

2. GI

3. through the skin, especially damaged

Working with opened sources of IR may lead to gas emanation which occurs after radioactive

decay:

1. Radium

2. Uranium

3. Thorium, etc

A part of radioactive substances [RS] are excreted with urine, faeces, saliva, sweat. Another part

is circulating in blood & deponates in other organs & tissues. Deponated RS after their decay

may create new “daughter” RS (usually it concerns Uranium, Thorium, Actinium- natural

radionuclides).

The reaction on the IR depends on the age & general state of the human organism. It is known

that between the age 35-50 years people are relatively low radiosensitive.

CRES: is the general chronic disease which develops in the result of continuous multiple action

of IR in respectively small doses of radiation (more than 0,01Rad/daily).

Types of CRES:

1. CRES from external irradiation

2. CRES from internal irradiation

3. CRES from mixed irradiation

Stages of CRES:

1 stage:

The mildest form include: functional changes in the organism, a lot of patient’s complains, but

poor symptoms during inspection.

Headaches

Progressive malaise (weekness)

Memory loss

Decreased appetite

Increased heart rate

Insomnia, or increased sleepiness, sleep inversion

Inspection:

Vasomotor unstableness

Red dermography

Sweating

Increased periostal reflexes

Light tremor of eyelids & fingers of the extended hand

Hypotonic tendency

All these symptoms are the compounds of the vegetative asthenia syndrome

Gastric secretion is decreased

Trophic skin changes, skin dryness & desquamation

Local epilation

Fingernails fragility

Menstrual cycle changes, menometrorrhagia, oligomenorrhea

Blood changes:

Brief primary phase of the bone marrow irritation: Leykocytosis, lymphocitosis, erythrocitosis,

reticulocytosis

Stage of the bone marrow depression: leikopenia (4-3,5x10

/L), lymphopenia, /or

neutropenia & relative lymphocitosis; there are quality changes of the blood cells: toxic

granularity of the neutrophils, hypersegmentation & fragmentation of the neutrophil’s nuclei,

lymphocyte’s nuclei picnosis, mild thrombocytopenia (160-140x10

/L)

Bone marrow puncture: delay of the myeloid cells development (maturation)

In this stage it’s usual to have increase of symptoms changing with recovery periods (wave-like

currency of the disease)

2 (intermediate) stage:

Increase of previous symptoms:

nausea

dizziness

vomiting

insomnia

decreased workability

dyspepsia: overinflation, diarrhoea, constipation

heart aches like angina pectoris

hemorrhagic diathesis

subdermal haematoma

gums & nasal bleeding

Inspection:

Increased periostal reflexes

Decreased abdominal reflexes

Decreased skin sensitivity & muscular tonus

Diencephal syndrome: have a cyclic currency (improvement changes into worsening)

Tachycardia paroxysm

Fever, heat

Cold limbs

Subfebril temperature

Metabolic & trophic disorders

BP stable decrease, arrythmias, irregular pulse, muffled & thuded heart tones

Hypertensive syndrome due to increased cerebral & liquor circulation:

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nausea



dizziness



vomiting



headache



loss of consciousness



sluggishness of the eye bottom



Increase of the spinal liquid tissue (differential diagnostics with brain tumors)

Gastric achilia

Decrease of the enzymal activity: amylase, trypsynum, lipase

Endocrine dysfunction: menorragia, dysmenorrhea, amenorrhea, hot flashes

Sterility in male

Adrenal glands: hypotension, weakness

Impaired thyroid function→subfebrile temperature

Blood changes:



stable leikopenia (1.5-2.5x10

/L), neutropenia & relative lymphocitosis; monocytosis



there are quality changes of the white blood cells: nuclei & protoplasm vacuolisation, cellular

decay



thrombocytopenia (less than 100x10

/L), bleeding time increases, blood coagulation delayed



Bone marrow puncture: bone marrow depression, delay of the myeloid , megacaryocitic &

erythroblastic cells development (maturation)



Depression of the organism resistance to infections

Changes in this stage are not only functional but organic

Poor prognosis, recovery cannot be complete

III stage:

Organic changes:



Weakness



Adynamia



Apathy



Constant headaches



nausea



dizziness



vomiting



Memory loss



Insomnia, or increased sleepiness, sleep inversion



Depression of the organism resistance to infections → chronic sepsis

CNS:



Disseminated encephalomyelitis or funicular myelosis: changes in the motor, sensitive &

reflex activity

Severe changes in the GIT, endocrine & cardiovascular systems

All types of metabolic changes (protein, lipid, mineral, carbohydrate)

Increased proteins decay which leads to cachexy

Blood changes:



stable leikopenia (1.5-1,0x10

/L & less), neutropenia & lymphopenia;

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hyperchromic anemia, RBC sedimentation rate increases

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thrombocytopenia (less than 30x10

/L), bleeding time increases, blood coagulation delayed



Bone marrow puncture: hypoplasia, delay of the myeloid , megacaryocitic & erythroblastic

cells development (maturation), in some cases there are conversion of the erythropoiesis into

megaloblastic type



Depression of the organism resistance to infections



Currency of the disease is progressive



Prognosis fatal

Peculiarities of the CRES due to ingestion of the RS:

Absence of initial reaction symptoms

latent period is not indicated

hemorrhagic syndrome may be absent

usually there is no epilation

manifest GIT or respiratory symptoms

nasal, pharyngeal & eye symptoms

extensive functional & organic changes in the organs of the selective accumulation of

radionuclides

The clinical course depends on the:

half-decay period, half-excretion time

chemical structure of the RS

the way of RS distribution & ways of excretion

RS with long half-decay period result in continuous irradiation & progression of the disease.

If RS get into the organism through the respiratory route they may be represented by gases,

dust & vapour.

Dust may be deposited in alveoli only if its less than 5 mkm in diameter, it may spread into

circulation in d less than 1 mkm & then becomes deposited in any organ.

RS which got into the upper respiratory tract cause hyperemia & edema, then atrophy of the

nasal & pharyngeal mucosa→ chronic rhinitis, pharyngitis, tracheitis.

GIT: RS which get into the GIT are easily secreted into the bloodstream & are deposited in some

organs according to the tropism of RS. For example: Strontium is deposited in bones→ leads to

osteitis & radiation necrosis, osteomyelitis which may be fatal. Usually osteonecrosis happen in

the flat bones- jaw, vertebras. Usually such patients have symptoms of gingivitis.

After longer period of time malignant tumors may develop such as osteogenic sarcomas. If

patient have incorporated radionuclides he may develop bone & muscle pain during walk & at

rest (the most usual location- sternal bone & shank.

Diagnostics of the CRES:

dosimeter data

professional groups

CRES is usually revealed in persons who received the total dose of more than 1,5 Gy.

Treatment of CRES:

Give up contact with RS

Maximal staying at opened-air areas

Medicines according to the selective accumulation of radionuclides