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radiation_injury [2020/02/22 11:03] (current)
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 +====== radiation injury ======
 +see also:
 +  *[[radiation_ionising|ionising radiation]]
 +  *[[oncology]]
 +  *[[radiation_emergencies|radiation emergencies]]
 +  *[[polonium]]
 +=====Radiation syndromes:​=====
 +====haemopoietic syndrome:​====
 +  *bone marrow suppression results from exposures > 1Sv (Sievert)
 +  *0.25Sv is the lowest dose to cause detectable effects on lymphocyte count¬†
 +  *1Sv causes nausea & fatigue, mild haemopoietic syndrome in 50% of exposed
 +  *2Sv causes nausea, loss of body hair & possible death from haempoietic syndrome
 +  *3Sv whole body acute exposure results in:
 +    *prodromal phase lasting 2 days:
 +      *transient rise in neutrophils
 +      *fall in neutrophil & lymphocyte counts
 +    *latent phase from D2-20:
 +      *moderate neutropenia,​ lymphopenia,​ falling platelets & Hb
 +    *acute illness - bone marrow depression phase D20-40:
 +      *severe neutropenia,​ lymphopenia,​ thrombocytopenia & falling Hb
 +      *risk of death mainly due to secondary infection, bleeding, poor wound healing
 +    *recovery phase or death D40-60:
 +      *return of cell counts to normal
 +  *4Sv causes death in 50% of those exposed
 +  *6Sv causes death in most people exposed
 +====gastrointestinal syndrome:​====
 +  *loss of crypt intestinal stem cells & mucosal barrier occurs due to exposures > 10Sv
 +    * however, the stem cells normally produce billions of daughter cells each day and these can de-differentiate back into stem cells if the patient can be kept alive for a week and there is no ongoing radiation injury (([[https://​​news/​2020-02-scientists-long-debated-puzzle-intestine.html]]))
 +  *fluid & electrolyte loss, sepsis, probable death within 2wks
 +====cerebrovascular syndrome:​====
 +  *microvascular injury due to exposures > 20Sv
 +  *LOC a few minutes after exposure, brain damage then certain death within days
 +=====Mx of acute radiation syndrome:​=====
 +  *treat life-threatening injuries
 +  *survey for radiological contamination and decontaminate
 +  *consider decorporation of absorbed or ingested radiological contaminants
 +  *supportive care in reverse isolation
 +  *5-HT3 antagonists for vomiting (eg. metoclopramide,​ ondansetron)
 +  *early consultation with haematologists & health physicists re:
 +    *dosimetry & prognosis
 +    *use of colony stimulating factors (CSFs)
 +    *stem cell transfusion
 +    *other Rx options
 +  *prevention & Rx of infections
 +  *observe carefully for erythema, hair loss, skin injury - if possible, take photographs
 +  *psychological support
 +  *Ix:
 +    *FBE then absolute lymphocyte counts 6hrly for 48hrs to assess radiation dose, & degree of injury
 +    *urinalysis to establish baseline
 +    *swabs from body orifices to assess possibility of internal radioactive contamination
 +    *wound dressing or wound swabs to determine if wounds are contaminated
 +    *24hr urine  x 4 days & faeces x 4 days as excreta may contain evidence of internal contamination
 +  *RSP follow up:
 +    *collection of personal data for entry into DHS emergency database, including charts detailing areas of significant contamination
 +    *assist with psychological counseling to put risks in perspective
 +=====Acute local injury from radiation:​=====
 +====skin burns:====
 +  *Burns occur at exposures above 10Sv (erythema at lower doses)
 +  *eg. an 8hr exposure to a piece of radioactive metal placed in a pocket caused initial erythema & blistering with evolving spreading necrosis which by 2mths had necrosed approx. 30cm diameter region of the thigh requiring amputation of the limb.
 +====hair loss:====
 +  *may be apparent 2wks or so after exposures > 3Sv
 +====fertility impairment:​====
 +  *300mSv to testes causes temporary sterility in men
 +  *3Sv to ovaries induces permanent sterility on women
 +  *presumed risk of induction of severe genetic effects in offspring based on animal studies is 8-10 in a million per mSv exposure
 +=====Late somatic effects from radiation exposure:​=====
 +  *see also: [[Neoplasia]]
 +  *the natural risk of dying from cancer is 1 in 4
 +  *the additional risk of dying from cancer due to radiation exposure is ~ 5/​100,​000ths per mSv exposure
 +  *atomic bomb data in Japan for solid cancers:
 +    *approx. linear increase in rate of cancers with colon dose such that a 0.75Sv colon dose caused a 20-40% increase in cancer rate, while a 2Sv exposure caused a 40-100% increase in rate (ie. double the normal rate of cancer)
 +  *examples of chronic exposure or late effects of acute exposure:
 +    *XS X-ray => skin cancer
 +    *ingestion luminous paints containing radium (alpha) => stomach cancer;
 +    *surface beta-ray seems to only cause skin burns & hair loss;
 +    *ingested Sr90 (beta) in fallout => replaces Ca in bones => insidious!!
 +    *fast neutrons => eye cataracts as high RBE;
 +=====Cell damage:​=====
 +====Individual cell damage:====
 +  *Measurement of cellular radiation effects is based on the "​survival curve" which shows the % of cells still able to multiply (on a log scale) vs radiation dose (Gy) on linear scale;
 +  *For most radiations, there is an initial "​shoulder"​ on the curve where little damage is caused, as an accumulation of sub-lethal damage is necessary before an observable effect is seen, but once past this there is a relatively straight steep slope of rapidly reducing survival with increased dose.
 +  *The slope depends on the RBE & thus on:
 +    ***LET:**
 +      *av. amount of energy deposited per micron of track;
 +      *This is important as the greater the no. of ionisations grouped closely together, the more likely to initiate a lethal chain of biological events & the less likely cellular repair mechanisms will act effectively;​
 +      *Depends on type of particle & energy of particle;
 +    ***OER:**
 +      *ratio of doses to reduce survival to same level in anoxic vs normal conditions;
 +      *presence of oxygen enhances ionisation damage by binding to freshly severed ends of molecular structures thus preventing them from rejoining;
 +    *Presence of other radio-sensitisers & radio-protectors;​
 +    *Time allowed for repair & recovery:
 +      *If some hours are allowed to elapse to allow cells to repair, the shoulder must again be passed.
 +====Tissue radiation effects:​====
 +  *As cell function not related to mitosis & division is relatively insensitive to radiation requiring large doses to produce these other cell functions, the typical radiation effect on tissues arises from inhibition of cell division.
 +  *Thus, tissues whose cells are continuously undergoing controlled division to maintain integrity are therefore the first tissues to show effects of radiation:
 +    *skin, GIT, bone marrow, immune system, malignant tumours;
 +  *The initial effect is a reduction in cell numbers as the supply of new cells falls, this leads via homeostatic feedback mechanisms to a build up of the population stem-cells & to an increase in rate of cell division. If successful, the depleted population is restored, often with a temporary hyperplasia or overshooot.
 +  *There may be an inflammatory response which may result in fibrosis;
 +  *If the cell population falls below a critical level (eg. 8 Gy to bone marrow or 12Gy to GIT), the tissue can lose its functional effectiveness which may result in death of the individual;
 +  *If the limit of tolerance is reached, there is an accumulation of permanent irreparable damage (eg. 18Gy);
 +  *Cells that are long-lived & not dividing (eg. adult liver, thyroid, long-lived lymphocytes) show little effect after doses of several grays, but damage has been done & becomes apparent when the cells are stimulated to divide, even after long periods of time.
 +  *Damage to gonads may lead to infertility due to impairment of germ cell division. Mutations also occur & the rate is proportional to dose, & thus, there is no "​safe"​ level of background irradiation;​
 +  *Mutations in somatic cells may lead to tumours;
 +====Microscopic appearances:​====
 +  *Following a substantial dose, there is a latent period of hours or days before histologic evidence of tissue damage is seen.
 +  *Early changes in skin include dilatation of blood vessels, & other signs of acute inflammation reflecting tissue injury;
 +  *With a single dose of 15Gy, mitotic activity of basal cells arrested causing loss of epidermis & epilation. The walls of the dermal vessels are infiltrated with fibrin, later concentric proliferation of fibrous tissue is seen (endarteritis obliterans),​ followed by replacement with hyaline collagen. Large bizarre fibrocytic nuclei are present in dermal CT.
 +  *With repeated doses, the dermal collagen becomes very dense with tendency to necrosis even years after exposure. Persistent melanin pigmentation & vasc.dilatation noted;
 +====Fetal effects:​====
 +  *radiation exposure to a pregnant woman:
 +    *prior to implantation (ie. 1st 9 days post-conception) will result either in embryonic loss or complete recovery
 +    *15-50 days post-conception (ie. organogenesis phase) causes risk of:
 +      *neuropathology (peak incidence if exposure 1st half of this time period)
 +      *growth retardation
 +      *miscarriage
 +      *fetal malformations
 +      *carcinogenesis - increased risk of childhood cancer is thought to be 4-6 per 10,000 children per cGy exposure
 +      *thus max. allowable occupational radiation exposure to pregnant women is 0.5milliSievert/​month
 +    *> 50 days post-conception:​
 +      *as for 15-50 days BUT:
 +        *minimal risk of malformations & miscarriage
 +        *lower risk of neuropathology
 +        *similar risk of carcinogenesis & growth retardation
radiation_injury.txt · Last modified: 2020/02/22 11:03 (external edit)